Fucoidans as Ligands for the Diagnosis of Degenerative Pathologies

ABSTRACT

The present invention relates to the diagnosis of clinical conditions characterized by undesirable and/or abnormal selectin expression. In particular, the invention provides for the use of fucoidans for the detection of selectins using imaging techniques including ultrasonography, scintigraphy and MRI. Selectin-targeted imaging agents are provided that comprise at least one fucoidan moiety associated with at least one detectable moiety. Methods and kits are described for using these imaging agents in the diagnosis of clinical conditions such as thrombosis, myocardial ischemia/reperfusion injury, stroke and ischemic brain trauma, neurodegenerative disorders, tumor metastasis and tumor growth, and rheumatoid arthritis.

RELATED APPLICATION

The present patent application is a continuation-in-part of patentapplication Ser. No. 13/259,802, which was itself filed pursuant to 35U.S.C. §371 as a U.S. National Phase application of International PatentApplication No. PCT/IB32009/052791 filed on Apr. 10, 2009. The entirecontent of the PCT application and of the U.S. National Phaseapplication is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Numerous human degenerative diseases, including cardiovasculardegenerative diseases, but also organ-specific degenerative diseases,involve circulating cell/vascular wall interactions. Selectins areimportant cell adhesion molecules, with high affinities for carbohydratemoieties. They play a prominent and critical role in the initial stagesof circulating cellular components and vascular wall interactions bymediating leucocytes/platelet and leucocytes/endothelium interactions.Three types of selectins have been discovered so far: P-selectin,E-selectin and L-selectin. L-selectin is constitutively expressed onalmost all circulating leukocytes. The expression of E-selectin isinducible on vascular endothelium upon activation by various mediatorsincluding cytokines and endotoxin. P-selectin is contained inintracytoplasmic granules and is rapidly translocated to platelet orendothelial surfaces after cell exposure to thrombin or histamine.

The P-, L- and E-selectins are structurally similar transmembraneproteins. They all possess large, highly glycosylated, extracellulardomains, a single spanning transmembrane domain, and a small cytoplasmictail. At their extracellular amino termini, they have a singlecalcium-dependent (or C-type) lectin domain (L) followed by an epidermalgrowth factor (EGF)-like domain (E) and several complement regulatorydomains (C). Selectin-mediated cell adhesion results fromcalcium-dependent interactions of the amino-terminal lectin domain witha large variety of carbohydrate-presenting molecules on the surface oftarget cells. While the affinity of each of the selectins variesdepending on the ligand, they all bind a specific tetrasaccharidecarbohydrate structure known as sialyl Lewis X (SLe^(x)), which containssialic acid and fucose residues.

Although selectin-mediated binding events play a critical role in normalphysiological processes, selectins are also known to contribute to manypathologies. Such pathologies include clinical conditions that areassociated with platelet activation and fibrin formation such asatherothrombotic diseases (E. Galkina et al., Curr. Drug Targets, 2007,8: 1239-1248); clinical conditions associated with acute endothelialactivation such as sepsis, brain ischemia, or ischemia-reperfusion (C.R. Calvey et al., J. Invest. Surg., 2007, 20: 71-85); clinicalconditions associated with chronic endothelial activation such ashypertension, hyperlipidemia, obesity (S. Nishimura et al., J. Clin.Invest., 2008, 118: 710-721) and degenerative disorders of thecardiovascular system, the lung or the brain (M. Fisher, Rev. Neurol.Dis., 2008, 5 Suppl. 1: S4-S11; S. I. van Kasteren et al., Proc. Natl.Acad. Sci. USA, 2009, 106: 18-23); and clinical conditions associatedwith chronic focalized accumulation of leukocytes such as tertiarylymphoid neogenesis or autoimmune diseases. Selectin interactions canalso mediate adhesive mechanisms involved in the metastasis of certainepithelial cancers (I. P Witz, Immunol. Lett., 2006, 104: 89-93; 1; S.Gout et al., Clin. Exp. Metastasis, 2008, 25: 335-344; L. Borsig, ExpertRev. Anticancer Ther., 2008, 8: 1247-1255).

Selectins are considered as potentially useful markers for the diagnosisof some of these pathologies. Numerous efforts are in progress to imageselectins predominantly through Magnetic Resonance Imaging (MRI) (S.Bouty et al., Contrast Media Mol. Imaging, 2006, 1: 15-22), scintigraphy(G. Hairi et al., Ann. Biomed. Eng., 2008, 36: 821-830), and morerecently using ultrasons (F. S. Villanueva et al., Nat. Clin. Pract.Cardiovasc. Med., 2008, 5: S26-S32). Most selectin imaging agentsdeveloped so far are anti-selectin antibodies (B. A. Kaufman et al.,Eur. Heart J., 2007, 28: 2011-2017; G. Hairi et al., Ann. Biomed. Eng.,2008, 36: 821-830; K. Licha et al., J. Biomed. Opt., 2005, 10: 41205;and P. Hauff et al., Radiology, 2004, 231: 667-673) and sialyl Lewis Xanalogs or derivatives (S. Bouty et al., Contrast Media Mol. Imaging,2006, 1: 15-22; F. S. Villanueva et al., Circulation, 2007, 115:345-352). These imaging agents have been demonstrated to allow the invivo non-invasive detection of selectins in inflammation,neurodegenerative disorders, cancer and thrombosis. However, theyexhibit several disadvantages that will certainly preclude theirindustrial development and commercialization. Indeed, the preparationand purification of sialyl Lewis X-based imaging agents and ofantibody-based imaging agents is complex and very costly.

Therefore, there remains a need in the art for new approaches for theimaging and detection of circulating cell/vascular wall interactionsallowing the non-invasive diagnosis and/or the preventive screening ofdiseases such as cardio/neurovascular pathologies, neurodegenerativedisorders and cancer metastasis. Selectin imaging agents that are easyand relatively cheap to produce are particularly desirable.

SUMMARY OF THE INVENTION

The present invention relates to improved systems and strategies for thedetection of selectins and the diagnosis of diseases and disorderscharacterized by undesirable or abnormal interactions mediated byselectins. In particular, the invention encompasses the recognition bythe Applicants that fucoidans exhibit high affinity, specificity and/orselectivity for selectins. More specifically, the present Applicantshave compared the interactions of P-selectin with several low molecularweight (LMW) polysaccharides: fucoidan, heparin and dextran sulfate.Using binding assay, mass spectrometry, surface plasmon resonance andflow cytometry on human platelets, they found that LMW fucoidan is themost efficient ligand of P-selectin (see Example 1). However, a lessspecific binding of fucoidan to fibrin moieties through hydrogen bondsis not excluded (K. H. Hsieh, Biochemistry, 1997, 36: 9381-9387). TheApplicants also showed that LMW fucoidan radiolabelled withTechnetium-99m (^(99m)Tc) allowed the in vivo detection of endocarditicvegetations, aneurismal and atrial thrombi in animal models (conditionsassociated with platelet-selectin exposition and fibrin formation) (seeExample 2). The Applicants have also developed an MRI contrast agentcomprising fucoidan conjugated to USPIOs (ultra small superparamagneticiron-oxide nanoparticles) which, in a rat model of vascular injury, wasfound to allow visualization of platelet-rich thrombus with highsensitivity and excellent sensitivity, very soon after injection of thecontrast agent and requiring only a short image acquisition time(Example 6).

Accordingly, the present invention provides for the use of fucoidans forthe detection and imaging of selectins and for the diagnosis of diseasesand disorders characterized by undesirable or abnormal expression ofselectins.

More specifically, in one aspect, the present invention provides animaging agent comprising at least one fucoidan moiety associated with atleast one detectable moiety. Preferably, the imaging agent isselectin-targeted. More preferably, the at least one fucoidan moiety ofthe imaging agent binds to at least one human selectin selected from thegroup consisting of P-selectin, L-selectin, and E-selectin with adissociation constant of between about 0.1 nM and about 500 nM,preferably between about 0.5 nM and about 10 nM, more preferably betweenabout 1 nM and about 5 nM.

In certain embodiments, the detectable moiety comprises ametal-chelating moiety complexed to a detectable moiety.

In certain embodiments, the detectable moiety is detectable by planarscintigraphy (PS) or Single Photon Emission Computed Tomography (SPECT).For example, the detectable moiety is a radionuclide selected from thegroup consisting of technetium-99m (^(99m)Tc), gallium-67 (⁶⁷Ga),yttrium-91 (⁹¹Y), indium-111 (¹¹¹In), rhenium-186 (¹⁸⁶Re),) andthallium-201 (²⁰¹T1). In certain preferred embodiments, the detectablemoiety is technetium-99m (^(99m)Tc).

In other embodiments, the detectable moiety is detectable by PositronEmission Tomography (PET). For example, the detectable moiety may beselected from the group consisting of carbon 11 (¹¹C), nitrogen-13(¹³N), oxygen-15 (¹⁵O) and fluorine-18 (¹⁸F).

In other embodiments, the detectable moiety is detectable bycontrast-enhanced ultrasonography (CEUS). For example, the detectablemoiety may be selected from the group consisting of acoustically activemicrobubbles and acoustically active liposomes.

In still other embodiments, the detectable moiety is detectable byMagnetic Resonance Imaging (MRI). For example, the detectable moiety maybe selected from the group consisting of gadolinium III (Gd³⁺), chromiumIII (Cr³⁺), dysprosium III (Dy³⁺), iron III (Fe³⁺), europium (Eu³⁺),manganese II (Mn²⁺), and ytterbium III (Yb³⁺). In certain preferredembodiments, the detectable moiety is gadolinium III (Gd³⁺).Alternatively, the detectable moiety detectable by MRI may be anultrasmall superparamagnetic iron oxide particle (USPIO).

In yet other embodiments, the detectable moiety is detectable byfluorescence spectroscopy. For example, the detectable moiety may beselected from the group consisting of europium (Eu³⁺), quantum dots,Texas red, fluorescein isothiocyanate (FITC), phycoerythrin (PE),rhodamine, carboxycyanine, Cy-3, Cy-5, Cy5.5, Cy7, DY-630, DY-635,DY-680, Atto 565 dyes, merocyanine, styryl dye, oxonol dye, BODIPY dyes,and analogues, derivatives or combinations of these molecules. Inparticular, in certain embodiments, the detectable moiety is detectableby time-resolved fluorometry. For example, the detectable moiety may beeuropium (Eu³⁺).

In certain embodiments of the present invention, an imaging agent isdetectable by more than one imaging technique and may therefore be usedin multimodal imaging. For example, an imaging agent may be detectableby any suitable combination of imaging techniques selected from thegroup consisting of ultrasonography, Magnetic Resonance Imaging (MRI),Positron Emission Tomography (PET), Single Photon Emission ComputedTomography (SPECT), fluorescence spectroscopy, Computed Tomography, andX-ray radiography. In certain embodiments, such an imaging agentcomprises at least one fucoidan moiety associated with at least onedetectable moiety that is detectable by more than one imaging technique.In other embodiments, such an imaging agent comprises at least onefucoidan moiety associated with a first detectable moiety and a seconddetectable moiety, wherein the first detectable moiety is detectable bya first imaging technique and the second detectable moiety is detectableby a second imaging technique and the first and second imagingtechniques are different.

In certain embodiments, the fucoidan moiety has an average molecularweight of about 2000 to about 8000 Da. In other embodiments, thefucoidan moiety has an average molecular weight of about 20,000 to about70,000 Da. In yet other embodiments, the fucoidan moiety has an averagemolecular weight of about 100,000 to about 500,000 Da.

In another aspect, the present invention provides a pharmaceuticalcomposition comprising an effective amount of at least one imaging agentof the invention, or a physiologically tolerable salt thereof, and atleast one pharmaceutically acceptable carrier.

In a related aspect, the present invention provides for the use of animaging agent according to the invention for the manufacture of acomposition for the detection and/or imaging of selectins. The presentinvention also provides for the use of an inventive imaging agent forthe manufacture of a composition for the diagnosis of a clinicalcondition associated with selectins.

In still another aspect, the present invention provides a method fordiagnosing a clinical condition associated with selectins in a patient,said method comprising steps of: administering to the patient aneffective amount of an imaging agent, or a pharmaceutical compositionthereof, according to the invention; and detecting any selectin bound tothe imaging agent using an imaging technique.

In a related aspect, the present invention provides an imaging agentdisclosed herein for use in an in vivo method of diagnostic of clinicalconditions associated with selectins.

Examples of clinical conditions that can be diagnosed using an imagingagent and/or a method of the invention according to the invention aremembers of the group consisting of thrombosis, myocardialischemia/reperfusion injury, stroke and ischemic brain trauma,neurodegenerative disorders, tumor metastasis, tumor growth, andrheumatoid arthritis.

In yet another aspect, the present invention provides a method fordetecting the presence of abnormal selectins in a biological system, themethod comprising steps of: contacting the biological system with aneffective amount of an imaging agent, or a pharmaceutical compositionthereof, according to the invention; and detecting any selectin bound tothe imaging agent using an imaging technique. The biological sample maybe a cell, a biological fluid or a biological tissue.

In a related aspect, the present invention provides an imaging agentdisclosed herein for use in an in vitro method of diagnostic of clinicalconditions associated with selectins.

In certain embodiments, the biological sample originates from a patientsuspected of having a clinical condition associated with selectins, andthe method is used to diagnose the clinical condition.

In other embodiments, the biological sample originates from a patientwho has received a treatment for a clinical condition associated withselectins, and the method is used to monitor the response of a patientto the treatment.

In yet another aspect, the present invention provides kits for thediagnosis of a clinical condition associated with selectins in a patientor for the detection of abnormal selectins in a biological tissue, thekit comprising a selectin-targeted imaging agent according to theinvention or comprising a fucoidan moiety, a detectable moiety, andinstructions for preparing a selectin-targeted imaging agent describedherein using the fucoidan moiety and detectable moiety.

In certain embodiments, the detectable moiety is a short-livedradionuclide selected from the group consisting of technetium-99m(^(99m)Tc), gallium-67 (⁶⁷Ga), yttrium-91 (⁹¹Y), indium-111 (¹¹¹In),rhenium-186 (¹⁸⁶Re), and thallium-201 (²⁰¹T1).

The kit may further comprise instructions for diagnosing the clinicalcondition using the selectin-targeted imaging agent.

These and other objects, advantages and features of the presentinvention will become apparent to those of ordinary skill in the arthaving read the following detailed description of the preferredembodiments.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing inhibition of SLe^(x)P-selectin binding bysulfated polysaccharides. Binding of SLe^(x) polyacrylamide-biotin toP-selectin immobilized onto a microtiter plate was quantified bystreptavidin-peroxidase complexation and peroxidase reaction recorded at405 nm in the presence of increasing concentrations of dextran sulfate(▴), heparin (▪) and fucoidan (), as described in Example 1. Theresults of a representative experiment are shown [mean±SD (n≧3)].

FIG. 2 is a set of representative sensorgrams showing the associationand dissociation profiles of sulfated polysaccharides on immobilized IgGor P-selectin. Fucoidan (A), heparin (B) and dextran sulfate (C) wereinjected over SPR CM5 sensorchips on which were immobilized goatanti-human Fc IgG (grey recording, non specific control) plusP-selectin/Fc chimera (black recording). Kinetic studies were performedat a flow rate of 30 μL/min. Representative sensorgrams in resonanceunits (RU) are overlaid at a similar 1 μM concentration for all LMWsulfated polysaccharides. Dissociation constants were calculated using a1:1 Langmuir binding model plot (D) for the specific binding ofP-selectin with fucoidan (upper curve), heparin (lower curve) or dextransulfate (middle curve). Non-specific binding on IgG was observed foreach of the polysaccharides.

FIG. 3 is a graph showing the binding of FITC-coupled LMW fucoidan tohuman platelets in whole blood. FITC-coupled LMW fucoidan at 140 μM (1mg/mL) was incubated for 20 minutes at room temperature with citratedhuman blood diluted 10 times in PBS. Activation of platelets was inducedwith 2.5 μM ADP (medium activator; dotted line) or 200 μM TRAP (strongactivator; full line). Platelets were identified by their side andforward scatter and their positivity for a fluorolabeled specificplatelet antibody in flow cytometry. Binding of FITC-coupled LMWfucoidan to platelets was detected on the FL1 channel. Similar resultswere obtained using two other donors.

FIG. 4 is a graph showing the binding inhibition of labeled CD62Pantibody to platelets in the presence of LMW fucoidan. CD62P antibodywas incubated in the presence or in the absence of non-labeled LMWfucoidan, as described in Example 1. Activation of platelets was inducedby 200 μM TRAP. Platelets were identified by their side and forwardscatter and their positivity for a fluorolabeled specific plateletantibody in flow cytometry. Binding to activated platelets ofnon-relevant PC5-labeled IgG antibody is reported for comparison. Thebinding of PC5-labeled CD62P antibody to platelets, observed on the FL4channel, significantly decreased in the presence of LMW fucoidan. Valuesof mean fluorescence intensity (MFI) were normalized to the valueobtained by incubation with non-relevant IgG alone. *p<0.05 between datawith CD62P alone with Student's t-test.

FIG. 5 shows histology (left) and autoradiography (right) sections ofhearts in rat model of left endocarditis with aortic valve vegetations.(A) One histologic section vegetation is restricted to the valve (3)whereas the aorta (1) and the sub-valvular myocardium (2) were normal.On the autoradiography, the signal from ^(99m)Tc-labelled fucoidan,injected in vivo, is exactly co-localized with the valvular vegetation.(B) A negative control of a myocardium without vegetation gives thebackground in autoradiography. (C) On the autoradiography, the signalfrom ^(99m)Tc-labelled fucoidan is exactly co-localized with thefibrinoid cuff surrounding the catheter.

FIG. 6 shows tomography-SPECT in vivo imaging (left), histology (middle)and autoradiography (right) section in rat model of atrial thrombus. Thetomography-SPECT shows retention of ^(99m)Tc-labelled fucoidan in therat left atrium. The histology results show that there is fibrinousthrombus in the atrial lumen with muscle on both sides. On theautoradiography, the signal from ^(99m)Tc-labelled fucoidan is localizedin the myocardium facing the thrombus.

FIG. 7 shows histology (left) and autoradiography (right) sections of anabdominal aortic aneurysm in a rat model of aneurismal thrombus. On theautoradiography, the signal from ^(99m)Tc-labelled fucoidan is localizedat the lumen/vessel wall interface where a thin thrombus (blue) islocalized on the histology picture.

FIG. 8 shows the blood clearance of ^(99m)Tc-USPIO-FUCO (n=4) in normalrats. After correction for residual activity in the injection site andradioactive decay, the results were expressed as the percentage ofadministered dose remaining in the blood pool as a function of time,assuming that the blood represents 6% of the body weight.

FIG. 9 shows a comparison between the radiological and pathologicalfindings at two different levels. In vivo MRI manifestation (a) beforeand (b) 60 minutes after venous injection of USPIO-FUCO on largeintraluminal thrombus. Ex vivo high resolution T2* weighted images werescanned using two different echo times: (c) TE=3.8 and (d) TE=9.2. Sixtyminutes after injection, in vivo MRI showed enhancement on the surfaceof intraluminal thrombus (b). Expression of P-selectin appeared as abrown colored region along the surface of thrombus including grooves ofthrombi (e), and magnified view of anti P-selectin stain (f) and shortTE T2* weighted images showed more similar distribution than that withlonger TE T2* weighted images on ex vivo. T2*WI before (g) and 60minutes after (h) injection of USPIO-Fuco in the other rat. A smallP-selectin positive thrombus (i, black arrow) localized at the origin ofa ligatured collateral artery corresponds to the region that showedsignal enhancement 60 minutes after injection of USPIO-FUCO (h).

FIG. 10 shows an overtime course of ΔSNE(%) for three different contrastagents injected in the model rats: the MRI agent Sinerem from GuerbertS. A. (triangles), which are USPIO coated with neutral dextran; ironoxide particles coated with dextran (squares); and USPIO-FUCO (circles).Overtime course of ΔSNE(%) for USPIO-FUCO at the site of thrombuspathologically confirmed the correspondence. Pre-contrast MRI wasscanned 15 minutes before injection. Fifteen minutes after, USPIO-FUCOshowed statistically significant attenuation compared to the baseline(*p<0.05, **p<0.001).

FIG. 11 shows the time table of the variation of the Contrast to NoiseRatio (CNR) before (0-120 minutes) and after (120-185 minutes) injectionof USPIO-FUCO. During the first period (0-120 min), the injection ofUSPIO-CMD (CarboxyMethyl Dextran=control) did not modify the CNR. Incontrast, during the second period (120-185 min), the injection ofUSPIO-FUCO significantly negativates the RMN signal.

FIG. 12(A) shows the effects of different contrast agents on aorta withor without thrombus measured by MRI 60 minutes after injection. At thesite of thrombus, the Group that had received USPIO-FUCO showedsignificantly strong area reduction compared to the Group that hadreceived USPIO-CMD (p<0.001). In aorta without thrombus, there was nosignificant luminal reduction irrespective of the contrast agents used.Cf. Thrombus (−) group; CMD, 3.88±0.23: FUCO, 3.89±0.88, Thrombus (+)group; CMD, 1.15±0.48: FUCO, 38.53±24. FIG. 12(B) shows a scatter plotof thrombus thickness measured by MR Imaging and by histology. A strongcorrelation was observed, (r²=0.90) between the two methods withconsistent overestimation of ILT thickness using MRI. Thickness onhistology=−103.79-0.83×Thickness on MR.

FIG. 13 shows a confirmation of histological data by electronmicroscopy. TEM confirmed the histological data showing (A) areas ofplatelet/fibrin-rich material and hemagglutination areas in which RedBlood Cell (RBC) predominated. PolyNuclear Neutrophils (PNNs)predominated in platelet/fibrin-rich areas. Hyperdense iron signalpredominated in platelet/fibrin areas (square). The presence of iron wasconfirmed by more powerful enlargement (B, TEM image), Iron energyfiltered TEM (EFTEM) evidencing iron cores in white (C) and (D) mergedimage (red: iron).

DEFINITIONS

Throughout the specification, several terms are employed that aredefined in the following paragraphs.

As used herein, the term “selectin” has its art understood meaning andrefers to any member of the family of carbohydrate-binding,calcium-dependent cell adhesion molecules that are constitutively orinductively present on the surface of leukocytes, endothelial cells orplatelets. The term “E-selectin”, as used herein, has its art understoodmeaning and refers to the cell adhesion molecule also known as SELE,CD62E, ELAM, ELAM1, ESEL, or LECAM2 (Genbank Accession Numbers for humanE-selectin: NM_(—)000450 (mRNA) and NP_(—)000441 (protein)). As usedherein, the term “L-selectin” has its art understood meaning and refersto the cell adhesion molecule also known as SELL, CD62L, LAM-1, LAM1,LECAM1, LNHR, LSEL, LYAM1, Leu-8, Lyam-1, PLNHR, TQ1, or hLHRc (GenbankAccession Numbers for human L-selectin: NM_(—)000655 (mRNA) andNP_(—)000646 (protein)). The term “P-selectin”, as used herein, has itsart understood meaning and refers to the cell adhesion molecule alsoknown as a SELP, CD62, CD62P, FLJ45155, GMP140, GRMP, PADGEM, or PSEL(Genbank Accession Numbers for human P-selectin: NM_(—)003005 (mRNA) andNP_(—)002996 (protein)).

As used herein, the term “imaging agent” refers to a compound that canbe used to detect specific biological elements (e.g., biomolecules)using imaging techniques. Imaging agents of the invention are moleculescomprising at least one fucoidan moiety associated with at least onedetectable moiety. Imaging agents of the present invention can be usedto detect selectins in in vitro and ex vivo biological systems as wellas in subjects.

The term “fucoidan moiety” refers to any fucoidan entity exhibiting highaffinity, specificity and/or selectivity for selectins. In the contextof the present invention, when a fucoidan moiety is part of a molecule(e.g., an imaging agent), it confers itsspecificity/selectivity/affinity properties to the molecule, and themolecule becomes “selectin-targeted” (i.e., the molecule specificallyand/or efficiently interacts with and/or binds to selectins).

The terms “binding affinity” and “affinity” are used hereininterchangeably and refer to the level of attraction between molecularentities. Affinities can be expressed quantitatively as a dissociationconstant (K_(d) or K_(D)), or its inverse, the association constant(K_(a) or K_(A)).

The term “detectable moiety”, as used herein refers to any entity which,when part of a molecule, allows visualization of the molecule, forexample using imaging techniques.

The terms “pathological condition associated with selectins”, “diseaseassociated with selectins” and “disorder associated with selectins” areused herein interchangeably. They refer to any disease conditioncharacterized by undesirable or abnormal selectin-mediated interactions.Such conditions include, for example, disease conditions associated withor resulting from the homing of leukocytes to sites of inflammation, thenormal homing of lymphocytes to secondary lymph organs, the interactionof platelets with activated endothelium, platelet-platelet andplatelet-leukocyte interactions in the blood vascular compartment, andthe like. Examples of such disease conditions include, but are notlimited to, tissue transplant rejection, platelet-mediated diseases(e.g., atherosclerosis and clotting), hyperactive coronary circulation,acute leukocyte-mediated lung injury (e.g., adult respiratory distresssyndrome—ARDS), Crohn's disease, inflammatory diseases (e.g.,inflammatory bowel disease), autoimmune diseases (e.g., multiplesclerosis, myasthenia gravis), infection, cancer (including metastasis),thrombosis, wounds and wound-associated sepsis, burns, spinal corddamage, digestive tract mucous membrane disorders (e.g., gastritis,ulcers), osteoporosis, rheumatoid arthritis, osteoarthritis, asthma,allergy, psoriasis, septic shock, stroke, nephritis, atopic dermatitis,frostbite injury, adult dysponoea syndrome, ulcerative colitis, systemiclupus erythrematosis, diabetes and reperfusion injury following ischemicepisodes.

As used herein, the term “subject” refers to a human or another mammal(e.g., mouse, rat, rabbit, hamster, dog, cat, cattle, swine, sheep,horse or primate). In many embodiments, the subject is a human being. Insuch embodiments, the subject is often referred to as an “individual”,or to a “patient” if the subject is afflicted with a disease or clinicalcondition. The terms “subject”, “individual” and “patient” do not denotea particular age, and thus encompass adults, children and newborns.

The term “biological sample” is used herein in its broadest sense. Abiological sample is generally obtained from a subject. A sample may beof any biological tissue or fluid that can produce and/or containselectins. Frequently, a sample will be a “clinical sample”, i.e., asample derived from a patient. Such samples include, but are not limitedto, bodily fluids which may or may not contain cells, e.g., blood,urine, saliva, cerebrospinal fluid (CSF), cynovial fluid, tissue or fineneedle biopsy samples, and archival samples with known diagnosis,treatment and/or outcome history. Biological samples may also includesections of tissues such as frozen sections taken for histologicalpurposes. The term “biological sample” also encompasses any materialderived by processing a biological sample. Derived materials include,but are not limited to, cells (or their progeny) isolated from thesample, proteins or other molecules extracted from the sample.Processing of a biological sample may involve one or more of:filtration, distillation, extraction, concentration, inactivation ofinterfering components, addition of reagents, and the like.

The term “effective amount”, when used herein in reference to aselectin-targeted imaging agent of the invention, or a pharmaceuticalcomposition thereof, refers to any amount of the imaging agent, orpharmaceutical composition, which is sufficient to fulfill its intendedpurpose(s) (e.g., the purpose may be the detection and/or imaging ofselectins present in a biological system or in a subject, and/or thediagnosis of a disease associated with selectins).

A “pharmaceutical composition”, as used herein, is defined as comprisingat least one selectin-targeted imaging agent, or a physiologicaltolerable salt thereof, and at least one pharmaceutically acceptablecarrier.

The term “physiologically tolerable salt” refers to any acid addition orbase addition salt that retains the biological activity and propertiesof the free base or free acid, respectively, and that is notbiologically or otherwise undesirable. Acid addition salts are formedwith inorganic acids (e.g., hydrochloric, hydrobromic, sulfuric, nitric,phosphoric acids, and the like); and organic acids (e.g., acetic,propionic, pyruvic, maleic, malonic, succinic, fumaric, tartaric,citric, benzoic, mandelic, methanesulfonic, ethanesulfonic,p-toluenesulfonic, salicylic acids, and the like). Base addition saltscan be formed with inorganic bases (e.g., sodium, potassium, lithium,ammonium, calcium, magnesium, zinc, aluminum salts, and the like) andorganic bases (e.g., salts of primary, secondary, and tertiary amines,substituted amines including naturally occurring substituted amines,cyclic amines and basic ion exchange resins, such as isopropylamine,trimethylamine, diethylamine, triethylamine, tripropylamine,ethanolamine, 2-dimethylaminoethanol, 2-diethylaminoethanol,trimethamine, dicyclohexylamine, lysine, arginine, histidine, caffeine,procaine, hydrabamine, choline, betaine, ethylenediamine, glucosamine,methylglucamine, theobromine, purines, piperazine, piperidine,N-ethylpiperidine, polyamine resins, and the like).

As used herein, the term “pharmaceutically acceptable carrier” refers toa carrier medium which does not interfere with the effectiveness of thebiological activity of the active ingredients and which is notexcessively toxic to the hosts at the concentrations at which it isadministered. The term includes solvents, dispersion media, coatings,antibacterial and antifungal agents, isotonic agents, adsorptiondelaying agents, and the like. The use of such media and agents forpharmaceutically active substances is well known in the art (see, forexample, Remington's Pharmaceutical Sciences, E. W. Martin, 18^(th) Ed.,1990, Mack Publishing Co., Easton, Pa).

The term “treatment” is used herein to characterize a method or processthat is aimed at (1) delaying or preventing the onset of a disease orcondition (e.g., a selectin-associated state or condition); (2) slowingdown or stopping the progression, aggravation, or deterioration of thesymptoms of the state or condition; (3) bringing about amelioration ofthe symptoms of the state or condition; and/or (4) curing the state orcondition. A treatment may be administered prior to the onset of thedisease, for a prophylactic or preventive action. Alternatively oradditionally, a treatment may be administered after initiation of thedisease or condition, for a therapeutic action.

The terms “approximately” and “about”, as used herein in reference to anumber, generally include numbers that fall within a range of 10% ineither direction of the number (greater than or less than the number)unless otherwise stated or otherwise evident from the context (exceptwhere such a number would exceed 100% of a possible value).

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS

As mentioned above, the present invention is directed to the use offucoidans for the imaging of selectins and the diagnosis ofpathophysiological conditions associated with selectins. In particular,the invention encompasses imaging agents, kits and strategies forspecifically detecting the presence of selectins in vitro, ex vivo aswell as in vivo using imaging techniques.

I—Selectin-targeted Imaging Agents

In one aspect, the invention relates to a new class of imaging agentsthat have high affinity and specificity for selectins. Morespecifically, selectin-targeted imaging agents are provided thatcomprise at least one fucoidan moiety associated with at least onedetectable moiety.

Fucoidan Moieties

Fucoidans (also called fucosans or sulfated fucans) are sulfatedpolysaccharides with a wide spectrum of biological activities, includinganticoagulant, antithrombotic, antivirus, antitumor, immunomodulatory,anti-inflammatory, and antioxidant activities (B. Li et al., Molecules,2008, 13: 1671-1695; D. Logeart et al., J. Biomed. Mater Res., 1996, 30:501-508). Fucoidans are found mainly in various species of brown seaweed(B. Li et al., Molecules, 2008, 13: 1671-1695; M. Kusaykin et al.,Biotechnol. J., 2008, 3: 904-915). Variant forms of fucoidans have alsobeen found in marine animal species, including the sea cucumber. Thus,compared to other sulfated polysaccharides, fucoidans are widelyavailable from various kinds of cheap sources, and easily obtained usingmethods of extraction known in the art (C. Colliec et al.,Phytochemistry, 1994, 35(3): 697-700). These methods of extractiongenerally yield fucoidans with molecular weights in the 70-800 kDarange. Processes have also been developed to prepare low molecularweight fucoidans from high molecular weight fucoidans, e.g., lower thanabout 20 kDa (EP 0 403 377B, U.S. Pat. No. 5,321,133), or lower thanabout 10 kDa (EP 0 846 129 B; U.S. Pat. No. 6,028,191; A. Nardella etal., Carbohydr. Res., 1996, 289: 201-208).

Fucoidans are α-1,2- or α-1,3- linked L-fucose polymers that aresulfated on position 4 and position 2 or 3 following the glycosidiclinkage. However, besides fucose and sulfate residues, fucoidans alsocontain other monosaccharides (e.g., mannose, galactose, glucose,xylose, etc) and uronic acid groups. It is known in the art that thestructure of fucoidans from different brown algae varies from species tospecies. Furthermore, the structure of fucoidans can also be chemicallymodified. For example, methods have been developed to increase thepercentage of sulfate groups of fucoidans in order to obtainoversulfated fucoidans or fucoidan fragments (T. Nishino et al.,Carbohydr. Res., 1992, 229: 355-362; S. Soeda et al., Thromb. Res.,1993, 72: 247-256).

Fucoidan moieties suitable for use in the present invention are fucoidanmoieties that have some degree of attraction for selectins and can playa targeting role when comprised in an imaging agent. Preferably,fucoidan moieties are stable, non-toxic entities that retain theiraffinity/specificity/selectivity properties under in vitro and in vivoconditions. In preferred embodiments, fucoidan moieties exhibit highaffinity and specificity for selectins, i.e., they specifically andefficiently interact with, bind to, or associate with selectins.Suitable fucoidan moieties include fucoidans that exhibit affinity andspecificity for only one of the selectins (i.e., for L-selectin,E-selectin or P-selectin) as well as fucoidans that exhibit affinity andspecificity for more than one selectin, including those moieties whichcan efficiently interact with, bind to or associate with all threeselectins. Preferably, the interaction between a selectin and a fucoidanmoiety within an imaging agent is strong enough for at least the timenecessary for selectin detection using an imaging technique. In certainembodiments, a suitable fucoidan moiety interacts with a selectin,preferably a human selectin, with a dissociation constant (K_(d))between about 0.1 nM and about 500 nM, preferably between about 0.5 nMand about 10 nM, more preferably between about 1 nM and about 5 nM.

The design of an inventive imaging agent will be dictated by itsintended purpose(s) and the properties that are desirable in theparticular context of its use. Thus, fucoidan moieties will be chosenbased on their known, observed or expected, properties. For example, inembodiments where an imaging agent of the invention is to be used in thediagnosis of neurodegenerative disorders characterized by undesirable orabnormal selectin-mediated interactions in the brain, the imaging agentwill preferably be capable of crossing the blood-brain barrier.Therefore, such an imaging agent will preferably contain a fucoidanmoiety of low molecular weight (e.g., 2-8 kDa or lower than 5 kDa). Incontrast, an imaging agent containing a fucoidan moiety of highmolecular weight will be suited for situations in which the agent is tobe used, for example to image selectins in the vascular system. Indeed,because of its high molecular weight, the imaging agent will not be ableto easily diffuse and will therefore more likely remain within thevascular system, thereby allowing a more selective targeting of thesystem of interest.

A fucoidan moiety of high molecular weight can also have the advantageof being able to carry a high number of detectable moieties, thusincreasing the sensibility of the imaging agent (i.e., allowing thedetection of lower concentrations of selectins). In addition to theirmolecular weight, fucoidan moieties may be selected based on theirsulfate content. By varying the sulfate content (either by selection ofnaturally-occurring fucoidans or by chemical modification), it may bepossible to modulate the specificity of the fucoidan moiety (andcorresponding imaging agent) for one of the selectins (L-selectin,E-selectin or P-selectin). It is known, for example, that binding to P-and E-selectins increases with the presence of sulfate groups on theligand (T. V. Pochechueva et al., Bioorganic & Medicinal ChemistryLetters, 2003, 13: 1709-1712).

Alternatively or additionally, a fucoidan moiety may be selected basedon its structure and, in particular, based on the presence of at leastone functional group that can be used (or that can be easily chemicallyconverted to a different functional group that can be used) to associatethe fucoidan moiety to a detectable moiety. Examples of suitablefunctional groups include, but are not limited to, carboxy groups,thiols, amino groups (preferably primary amines), and the like.

Detectable Moieties

In the context of the present invention, detectable moieties areentities that are detectable by imaging techniques such asultrasonography, Magnetic Resonance Imaging (MRI), Positron EmissionTomography (PET), Single Photon Emission Computed Tomography (SPECT),fluorescence spectroscopy, Computed Tomography, X-ray radiography, orany combination of these techniques. Preferably, detectable moieties arestable, non-toxic entities which, when part of a selectin-targetedimaging agent, retain their properties under in vitro and in vivoconditions.

Radioactive Imaging Moieties. In certain embodiments, theselectin-targeted imaging agent is designed to be detectable by anuclear medicine imaging techniques such as planar scintigraphy (PS),Positron Emission Tomography (PET) and Single Photon Emission ComputedTomography (SPECT). In such embodiments, the imaging agent of theinvention comprises at least one fucoidan moiety associated with atleast one radionuclide (i.e., a radioactive isotope).

SPECT and PET have been used to detect tumors, aneurysms, irregular orinadequate blood flow to various tissues, blood cell disorders, andinadequate functioning of organs, such as thyroid and pulmonary functiondeficiencies. Both techniques acquire information on the concentrationof radionuclides introduced into a biological sample or a patient'sbody. PET generates images by detecting pairs of gamma rays emittedindirectly by a positron-emitting radionuclide. A PET analysis resultsin a series of thin slice images of the body over the region of interest(e.g., brain, breast, liver). These thin slice images can be assembledinto a three dimensional representation of the examined area. However,there are only few PET centers because they must be located near aparticle accelerator device that is required to produce the short-livedradioisotopes used in the technique. SPECT is similar to PET, but theradioactive substances used in SPECT have longer decay times than thoseused in PET and emit single instead of double gamma rays. Although SPECTimages exhibit less sensitivity and are less detailed than PET images,the SPECT technique is much less expensive than PET and offers theadvantage of not requiring the proximity of a particle accelerator.Planar scintigraphy (PS) is similar to SPECT in that it uses the sameradionuclides. However, PS only generates 2D-information.

Thus, in certain embodiments, the at least one detectable moiety in animaging agent of the invention is a radionuclide detectable by PET.Examples of such radionuclides include carbon-11 (¹¹C), nitrogen-13(¹³N), oxygen-15 (¹⁵O) and fluorine-18 (¹⁸F).

In other embodiments, the detectable moiety is a radionuclide detectableby planar scintigraphy or SPECT. Examples of such radionuclides includetechnetium-99m (^(99m)Tc), gallium-67 (⁶⁷Ga), yttrium-91 (⁹¹Y),indium-111 (¹¹¹In) rhenium-186 (¹⁸⁶Re), and thallium-201 (²⁰¹T1).Preferably, the radionuclide is technetium-99m (^(99m)Tc). Over 85% ofthe routine nuclear medicine procedures that are currently performed useradiopharmaceutical methodologies based on ^(99m)Tc. Therefore, incertain preferred embodiments, the at least one detectable moiety of animaging agent is ^(99m)Tc.

MRI Imaging Moieties. In certain embodiments, the selectin-targetedimaging agent is designed to be detectable by Magnetic Resonance Imaging(MRI). MRI, which is an application of Nuclear Magnetic Resonance (NMR),has evolved into one of the most powerful non-invasive techniques indiagnostic clinical medicine and biomedical research. It is widely usedas a non-invasive diagnostic tool to identify potentially maleficentphysiological anomalies, to observe blood flow or to determine thegeneral status of the cardiovascular system. MRI has the advantage (overother high-quality imaging methods) of not relying on potentiallyharmful ionizing radiation.

Thus, in certain embodiments, an imaging agent of the inventioncomprises at least one fucoidan moiety associated with at least oneparamagnetic metal ion. Examples of paramagnetic metal ions detectableby MRI are gadolinium III (Gd³⁺), chromium III (Cr³⁺), dysprosium III(Dy³⁺), iron III (Fe³⁺), manganese II (Mn²⁺), and ytterbium III (Yb³⁺).In certain preferred embodiments, the paramagnetic metal ion isgadolinium III (Gd³⁺). Gadolinium is an FDA-approved contrast agent forMRI.

In other embodiments, the imaging agent of the invention comprises atleast one fucoidan moiety associated with at least one ultrasmallsuperparamagnetic iron oxide (USPIO) particle. USPIO particles arecurrently under investigation as contrast agents for imaging humanpathologies (C. Corot et al., Adv. Drug Deliv. Rev., 2006, 56:1472-1504). They are composed of a crystalline iron oxide corecontaining thousands of iron atoms which provide a large disturbance ofthe Magnetic Resonance signal of surrounding water. In contrast to othertypes of nanoparticles such as quantum dots (currently underinvestigation as extremely sensitive fluorescent probes), USPIOparticles exhibit a very good biocompatibility. Chemical coating ofUSPIO particles is required to ensure their dispersion in biologicalmedia. The presence of an appropriate coating may also result in adecrease in the clearance of the particles (“stealth” effect) and mayprovide a means to bind these particles to molecules that are able totarget a specific tissue (R. Weissleder et al., Magn. Reson. Q, 1992, 8:55-63). Polysaccharides, such as dextran and its carboxymethylatedderivatives, are currently used as coatings.

USPIO particles are known in the art and have been described (see, forexample, J. Petersein et al., Magn. Reson. Imaging Clin. Am., 1996, 4:53-60; B. Bonnemain, J. Drug Target, 1998, 6: 167-174; E. X. Wu et al.,NMR Biomed., 2004, 17: 478-483; C. Corot et al., Adv. Drug Deliv. Rev.,2006, 58: 1471-1504; M. Di Marco et al., Int. J. Nanomedicine, 2007, 2:609-622). USPIO particles are commercially available, for example, fromAMAG Pharmaceuticals, Inc. under the tradenames Sinerem® and Combidex®.

The present invention proposes to coat USPIO particles with fucoidanmoieties and use the resulting imaging agents to detect selectins byMRI. Such inventive imaging agents may be particularly useful in thediagnosis of cardiovascular pathologies associated with selectins.Indeed, with a radius of about 15 nm, USPIO particles are likely todiffuse only weakly outside the vascular space with the exception ofmore permeable pathological vascular tissues such as atheroscleroticwalls. Therefore, they constitute a good blood pool agent (J. Bremerichet al., Eur. Radiol., 2007, 17: 3017-3024).

The present Applicants have developed USPIO-fucoidan nanoparticles thatproved to be efficient at detecting, by MRI, platelet-rich thrombus withhigh sensitivity and specificity (see Example 6). The nanoparticlesdeveloped by the Applicants have a mean diameter of about 65 mm andexhibit a core-shell structure, where the fucoidan moieties constitutethe outer shell of the particles. Consequently, the present inventionprovides an MR imaging agent under the form of USPIO particlesassociated with fucoidan moieties. In certain embodiments, the fucoidanmoieties have an average molecular weight of about 2000 to about 9000Da, e.g., about 5000, about 6000, about 7000 or about 8000 Da. In otherembodiments, the fucoidan moieties have an average molecular weight ofabout 10,000 to about 90,000 Da, e.g., about 20,000, about 30,000, about40,000, about 50,000, about 60,000, about 70,000 or about 80,000 Da. Inyet other embodiments, the fucoidan moieties have an average molecularweight of about 100,000 to about 500,000 Da. Preferably, USPIO-fucoidannanoparticles according to the present invention will be prepared suchthat the USPIOs are coated with fucoidan moieties and the resultingnanoparticles have a core-shell structure, the outer shell beingconstituted by the fucoidan moieties. In certain embodiments, aUSPIO-fucoidan nanoparticle according to the invention has a meandiameter between about 15 and about 100 nm, preferably between about 40and about 80 nm, more preferably between about 50 and about 70 nm.

Contrast-Enhanced Ultrasonography Imaging Moieties. In certainembodiments, the selectin-targeted imaging agent is designed to bedetectable by contrast-enhanced ultrasonography (CEUS). Ultrasound is awidespread technology for the screening and early detection of humandiseases. It is less expensive than MRI or scintigraphy and safer thanmolecular imaging modalities such as radionuclide imaging because itdoes not involve radiation.

Thus, in certain embodiments, the imaging agent of the inventioncomprises at least one fucoidan moiety associated with at least oneacoustically active (gas-filled) microbubble. A variety of acousticallyactive microbubbles may be used in the practice of the present invention(A. L. Klibanov, Bioconj. Chem., 2005, 16: 9-17; J. R. Lindner, Nat.Rev. Drug Discov., 2004, 3: 527-532; M. McCulloch et al., J. Am. Soc.Echocardiogr., 2000, 13: 959-967; A. M. Takalkar et al., J. Contr.Release, 2004, 96: 473-482; G. E. Weller et al., Biotechnol. Bioeng.,2005, 92: 780-788).

Generally, such microbubbles are comprised of a gas core and a shell.The gas core is the most important part of the microbubble because itallows detection. When gas bubbles are caught in an ultrasonic frequencyfield, they compress, oscillate and reflect a characteristic echo, whichgenerates a strong and unique sonogram in CEUS. Gas cores can becomposed of air, or heavy gases such as perfluorocarbon or nitrogen.Microbubbles with heavy gas-cores are likely to last longer in thecirculation compared to microbubbles with air-comprising cores. Theshell material determines how easily the microbubble is taken up by theimmune system. A microbubble with a shell made of a more hydrophilicmaterial tends to be taken up more easily by the immune system, while amore hydrophobic shell material tends to increase the microbubbleresidence time in the circulation, thus increasing the time availablefor contrast imaging. Microbubbles shells may be made of albumin,galactose, lipids or polymers (J. R. Lindner, Nat. Rev. Drug Discov.,2004, 3: 527-532). Regardless of the shell or gas core composition,microbubble size is fairly uniform. Their diameter is generally in the1-4 micrometer range. Therefore, they are smaller than red blood cells,allowing them to flow easily through the circulation as well as themicrocirculation (F. S. Vallanueva et al., Nat. Clin. Pract. Cardiovasc.Med., 2008, 5 Suppl. 2: S26-S32).

In other embodiments, the imaging agent of the invention comprises atleast one fucoidan moiety associated with at least one acousticallyactive lipid particle (i.e., a gas-filled liposome). A variety ofacoustically active lipid particles are known in the art and may be usedin the practice of the present invention (H. Alkan-Onyuksel et al., J.Pharm. Sci., 1996, 85: 486-490; S. M. Demos et al., J. Am. Coll.Cardiol., 1999, 33: 867-875; S. L. Huang et al., J. Pharm. Sci., 2001,90: 1917-1926; S. L. Huang et al., J. Ultrasound Med., 2002, 28:339-348; A. Hamilton et al., Circulation, 2002, 105: 2772-2778).

Fluorescence Imaging Moieties. In certain embodiments, theselectin-targeted imaging agent is designed to be detectable byfluorescence spectroscopy. In such embodiments, the imaging agents ofthe invention comprises at least one fucoidan moiety associated with atleast one fluorescent moiety.

Favorable optical properties of fluorescent moieties to be used in thepractice of the present invention include high molecular absorptioncoefficient, high fluorescence quantum yield, and photostability.Preferred fluorescent moieties exhibit absorption and emissionwavelengths in the visible (i.e., between 400 and 700 nm) or the nearinfra-red (i.e., between 700 and 950 nm). Selection of a particularfluorescent moiety will be governed by the nature and characteristics ofthe illumination and detection systems used in the diagnostic method. Invivo fluorescence imaging uses a sensitive camera to detect fluorescenceemission from fluorophores in whole-body living mammals. To overcome thephoton attenuation in living tissue, fluorophores with emission in thenear-infrared (NIR) region are generally preferred (J. Rao et al., CumOpin. Biotechnol., 2007, 18: 17-25). The list of NIR probes continues togrow with the recent addition of fluorescent organic, inorganic andbiological nanoparticles. Recent advances in imaging strategies andreporter techniques for in vivo fluorescence imaging include novelapproaches to improve the specificity and affinity of the probes, and tomodulate and amplify the signal at target sites for enhancedsensitivity. Further emerging developments are aiming to achievehigh-resolution, multimodality and lifetime-based in vivo fluorescenceimaging.

Numerous fluorescent moieties with a wide variety of structures andcharacteristics are suitable for use in the practice of the presentinvention. Suitable fluorescent labels include, but are not limited to,quantum dots (i.e., fluorescent inorganic semiconductor nanocrystals)and fluorescent dyes such as Texas red, fluorescein isothiocyanate(FITC), phycoerythrin (PE), rhodamine, fluorescein, carbocyanine, Cy-3™and Cy-5™ (i.e., 3- and 5-N,N′-diethyltetramethylindodicarbocyanine,respectively), Cy5.5, Cy7, DY-630, DY-635, DY-680, and Atto 565 dyes,merocyanine, styryl dye, oxonol dye, BODIPY dye (i.e., borondipyrromethene difluoride fluorophore), and analogues, derivatives orcombinations of these molecules.

In certain embodiments, the detectable moiety is detectable bytime-resolved fluorometry. For example, the detectable moiety iseuropium (Eu³⁺).

As will be understood by one skilled in the art, the selection of aparticular type of detectable moiety in the design of aselectin-targeted imaging agent will be dictated by the intended purposeof the imaging agent as well as by the imaging technique to be used inthe detection.

In certain embodiments, an imaging agent of the present invention may bedesigned to be detectable by more than one imaging technique, forexample by a combination of MRI-PET, MRI-SPECT, fluorescence-MRI, X-rayradiography-scintigraphy, and the like. Multimodal imaging providesdifferent types of information about biological tissues, such as bothstructural and functional properties. Thus, for example, an imagingagent according to the present invention may comprise at least onefucoidan moiety associated with at least one detectable moiety that isdetectable by more than one imaging technique. Examples of suchdetectable moieties include, but are not limited to, europium, which isfluorescent and detectable by MRI; and luminescent hybrid nanoparticleswith a paramagnetic Gd₂O₃ core that are developed as contrast agents forboth in vivo fluorescence and MRI (J. L; Bridot et al., J. Am. Chem.Soc., 2007, 129: 5076-5084) Alternatively, an imaging agent may compriseat least one fucoidan moiety associated with a first detectable moietyand a second detectable moiety, wherein the first detectable moiety isdetectable by a first imaging technique and the second detectable moietyis detectable by a second imaging technique. A large variety of imagingagents with double detectability may thus be obtained. The simultaneoususe of two different imaging agents (i.e., of a first imaging agentdetectable by a first imaging technique and a second imaging agentdetectable by a second imaging technique) is also contemplated.

Synthesis of Selectin-Targeted Imaging Agents

The inventive imaging agents may be prepared by any synthetic methodknown in the art, the only requirement being that, after reaction, thefucoidan moiety and detectable moiety retain their affinity anddetectability property, respectively. The fucoidan and detectablemoieties may be associated in any of a large variety of ways.Association may be covalent or non-covalent. When the association iscovalent, the fucoidan and detectable moieties may be bound to eachother either directly or indirectly (e.g., through a linker). When thedetectable moiety is a metal entity, the fucoidan moiety may beassociated to the detectable metal entity via a metal-chelating moiety.

More specifically, in certain embodiments, the fucoidan moiety anddetectable moiety are directly covalently linked to each other. Thedirect covalent binding can be through an amide, ester, carbon-carbon,disulfide, carbamate, ether, thioether, urea, amine or carbonatelinkage. The covalent binding can be achieved by taking advantage offunctional groups present on the fucoidan moiety and detectablemoieties. Suitable functional groups that can be used to attach the twomoieties together include, but are not limited to, amines (preferablyprimary amines), anhydrides, hydroxy groups, carboxy groups and thiols.A direct linkage may also be formed by using an activating agent, suchas a carbodiimide, to bind, for example, the primary amino group presenton one moiety to the carboxy group present on the other moiety.Activating agents suitable for use in the present invention are wellknown in the art.

In other embodiments, the fucoidan moiety and detectable moiety areindirectly covalently linked to each other via a linker group. This canbe accomplished by using any number of stable bifunctional agents wellknown in the art, including homofunctional and heterofunctional linkers.The use of a bifunctional linker differs from the use of an activatingagent in that the former results in a linking moiety being present inthe inventive imaging agent after reaction, whereas the latter resultsin a direct coupling between the two moieties involved in the reaction.The main role of the bifunctional linker is to allow the reactionbetween two otherwise chemically inert moieties. However, thebifunctional linker, which becomes part of the reaction product, canalso be selected such that it confers some degree of conformationalflexibility to the imaging agent (e.g., the bifunctional linker maycomprise a straight alkyl chain containing several atoms).

A wide range of suitable homofunctinal and heterofunctional linkersknown in the art can be used in the context of the present invention.Preferred linkers include, but are not limited to, alkyl and arylgroups, including straight chain and branched alkyl groups, substitutedalkyl and aryl groups, heteroalkyl and heteroaryl groups, that havereactive chemical functionalities such as amino, anhydride, hydroxyl,carboxyl, carbonyl groups, and the like.

Methods of direct or indirect covalent association may be used, forexample, in the synthesis of selectin-targeted imaging agents comprisinga fluorescent moiety. Similarly, such methods may be employed for thecoating of USPIO particles by fucoidan moieties (see Example 3), or tograft fucoidan onto acoustically active microbubbles or liposomes (seeExample 4).

In other embodiments, the fucoidan moiety and the detectable moiety aredirectly but non-covalently associated to each other. Non-covalentassociations include, but are not limited to, hydrophobic interactions,electrostatic interactions, dipole interactions, van der Waalsinteractions, and hydrogen bonding. For example, a fucoidan moiety and adetectable metal entity may be associated by complexation. Suitablecomplexation methods include, for example, direct incorporation of themetal entity into the fucoidan moiety and transmetallation. Whenpossible, direct incorporation is preferred. In such a method, anaqueous solution of the fucoidan moiety is generally exposed to or mixedwith a metal salt. The pH of the reaction mixture may be between about 4and about 11. Direct incorporation methods are well known in the art anddifferent procedures have been described (see, for example, WO87/06229). The present Applicants have shown that a low molecular weightfucoidan can easily be complexed to technetium-99m (see Example 2). Amethod of transmetallation is used when the metal entity needs to bereduced to a different oxidative state before incorporation.Transmetallation methods are well known in the art. It is to beunderstood that, given the short lifetime of certain radionuclides(e.g., ^(99m)Tc), the direct incorporation may have to be performedshortly prior to the use of the imaging agent.

When direct, non-covalent association between the fucoidan anddetectable metal moieties is not possible, the selectin-targeted imagingagent may comprise at least one fucoidan moiety associated with at leastone detectable moiety, wherein the detectable moiety comprises ametal-chelating moiety complexed to a detectable metal moiety. Theassociation between the fucoidan moiety and the metal-chelating moietyis preferably covalent. Suitable metal-chelating moieties for use in thepresent invention may be any of a large number of metal chelators andmetal complexing molecules known to bind detectable metal moieties.Preferably, metal-chelating moieties are stable, non-toxic entities thatbind radionuclides or paramagnetic metal ions with high affinity.

Examples of metal-chelating moieties that have been used for thecomplexation of paramagnetic metal ions, such as gadolinium III (Gd³⁺),include DTPA (diethylenetriaminepentaacetic acid); DOTA(1,4,7,10-tetraazacyclododecane-N,N′,N″,N′″-tetraacetic acid); andderivatives thereof (see, for example, U.S. Pat. Nos. 4,885,363;5,087,440; 5,155,215; 5,188,816; 5,219,553; 5,262,532; and 5,358,704;and D. Meyer et al., Invest. Radiol. 1990, 25: S53-55), in particular,DTPA-bis(amide) derivatives (U.S. Pat. No. 4,687,659). Othermetal-chelating moieties that complex paramagnetic metal ions includeacyclic entities such as aminopolycarboxylic acids and phosphorusoxyacid analogues thereof (e.g., triethylenetetraminehexaacetic acid orTTHA), and dipyridoxal diphosphate (DPDP) and macrocyclic entities(e.g., 1,4,7,10-tetraazacyclododecane-N,N′,N″-triacetic acid or DO3A).Metal-chelating moieties may also be any of the entities described inU.S. Pat. Nos. 5,410,043; 5,277,895; and 6,150,376; or in F. H. Arnold,Biotechnol. 1991, 9: 151-156.

Examples of metal-chelating moieties that complex radionuclides, such astechnetium-99m, include, for example, N₂S₂ and N₃S chelators (A. R.Fritzberg et al., J. Nucl. Med. 1982, 23: 592-598; U.S. Pat. Nos.4,444,690; 4,670,545; 4,673,562; 4,897,255; 4,965,392; 4,980,147;4,988,496; 5,021,556 and 5,075,099). Other suitable metal-chelatingmoieties can be selected from polyphosphates (e.g., ethylenediaminetetramethylenetetra-phosphonate, EDTMP); aminocarboxylic acids(e.g., EDTA, N-(2-hydroxy)ethylene-diaminetriacetic acid,nitrilotriacetic acid, N,N-di(2-hydroxyethyl)glycine,ethylenebis(hydroxyphenylglycine) and diethylenetriamine pentaceticacid); 1,3-diketones (e.g., acetylacetone, trifluoroacetylacetone, andthenoyltrifluoroacetone); hydroxycarboxylic acids (e.g., tartaric acid,citric acid, gluconic acid, and 5-sulfosalicyclic acid); polyamines(e.g., ethylenediamine, diethylenetriamine, triethylenetetraamine, andtriaminotriethylamine); aminoalcohols (e.g., triethanolamine andN-(2-hydroxyethyl)ethylenediamine); aromatic heterocyclic bases (e.g.,2,2′-diimidazole, picoline amine, dipicoline amine and1,10-phenanthroline); phenols (e.g., salicylaldehyde,disulfopyrocatechol, and chromotropic acid); aminophenols (e.g.,8-hydroxyquinoline and oximesulfonic acid); oximes (e.g.,hexamethylpropylene-amine oxime, HMPAO); Schiff bases (e.g.,disalicylaldehyde 1,2-propylenediimine); tetrapyrroles (e.g.,tetraphenylporphin and phthalocyanine); sulfur compounds (e.g.,toluenedithiol, meso-2,3-dimercaptosuccinic acid, dimercaptopropanol,thioglycolic acid, potassium ethyl xanthate, sodiumdiethyldithiocarbamate, dithizone, diethyl dithiophosphoric acid, andthiourea); synthetic macrocyclic compounds (e.g., dibenzo[18]crown-6),or combinations of two or more of the above agents.

As can readily be appreciated by those skilled in the art, aselectin-targeted imaging agent of the invention can comprise any numberof fucoidan moieties and any number of detectable moieties, linked toone another by any number of different ways. The fucoidan moietieswithin an inventive imaging agent may be all identical or different.Similarly, the detectable moieties within an inventive imaging agent maybe all identical or different. The precise design of a selectin-targetedimaging agent will be influenced by its intended purpose(s) and theproperties that are desirable in the particular context of its use

II—Uses of Selectin-Targeted Imaging Agents

The invention provides reagents and strategies to image and detect thepresence of selectins. More specifically, the invention providestargeted reagents that are detectable by imaging techniques and methodsallowing the detection, localization and/or quantification of selectinsin in vitro and ex vivo systems as well as in living subjects, includinghuman patients. The methods provided are based on the use ofselectin-targeted imaging agents comprising at least one fucoidan moietyhaving a high affinity and specificity for selectins, associated with atleast one detectable moiety that allows visualization of the imagingagent using imaging techniques.

More specifically, the present invention provides methods for detectingthe presence of selectins in a biological system comprising the step ofcontacting the biological system with an effective amount of aselectin-targeted imaging agent of the invention, or a pharmaceuticalcomposition thereof. The contacting is preferably carried out underconditions that allow the imaging agent to interact with selectinspresent in the system so that the interaction results in the binding ofthe imaging agent to the selectins. The imaging agent that is bound toselectins present in the system is then detected using an imagingtechnique. One or more images of at least part of the biological systemmay be generated. The contacting may be carried out by any suitablemethod known in the art. For example, the contacting may be carried outby incubation.

The biological system may be any biological entity that can produceand/or contain selectins. For example, the biological system may be acell, a biological fluid or a biological tissue. The biological systemmay originate from a living subject (e.g., it may be obtained by drawingblood, by biopsy or during surgery) or a deceased subject (e.g., it maybe obtained at autopsy). The subject may be human or another mammal. Incertain preferred embodiments, the biological system originates from apatient suspected of having a clinical condition associated withselectins.

The present invention also provides methods for detecting the presenceof selectins in a patient. The methods comprise administering to thepatient an effective amount of a selectin-targeted imaging agent of theinvention, or a pharmaceutical composition thereof. The administrationis preferably carried out under conditions that allow the imaging agent(1) to reach the area(s) of the patient's body that may contain abnormalselectins (i.e., selectins associated with a clinical condition) and (2)to interact with such selectins so that the interaction results in thebinding of the imaging agent to the selectins. After administration ofthe selectin-targeted imaging agent and after sufficient time haselapsed for the interaction to take place, the imaging agent bound toabnormal selectins present in the patient is detected by an imagingtechnique. One or more (e.g., a series) images of at least part of thebody of the patient may be generated. One skilled in the art will know,or will know how to determine, the most suitable moment in time toacquire images following administration of the imaging agent. Dependingon the imaging technique used (e.g., MRI), one skilled in the art willalso know, or know how to determine, the optimal image acquisition time(i.e., the period of time required to collect the image data).

The present Applicants have found that in contrast to what has beenreported concerning targeted USPIOs (Hyafil et al., Arterioscl. Thromb.Vasc. Biol., 2006, 26: 176-181), the selectin-targeted USPIO-fucoidannanoparticles according to the invention do no require an imageacquisition time of several hours. Indeed, they were able to show thatthe USPIO-fucoidan nanoparticles required less than 30 minutes of MRimage acquisition to depict with high sensitivity an intravenousthrombus in a rat model of vascular injury. Accordingly, in embodimentswhere USPIO-fucoidan nanoparticles according to the invention are usedto detect the presence of selectins in a patient or to diagnose apathological condition associated with selectins in a patient, themethods of the invention may further comprise a step of acquiring an MRimage for 1 hour or less than 1 hour, e.g., for 50 minutes, 45 minutes,40 minutes, 35 minutes, 30 minutes, 25 minutes, 20 minutes, 15 minutes,or less than 15 minutes. The MR image acquisition may start 30 minutesafter administration the USPIO-fucoidan nanoparticles to patient or morethan 30 minutes after such administration, e.g., 45 minutes, 60 minutesor 90 minutes.

Administration of the selectin-targeted imaging agent, or pharmaceuticalcomposition thereof, can be carried out using any suitable method knownin the art such as administration by oral and parenteral methods,including intravenous, intraarterial, intrathecal, intradermal andintracavitory administrations, and enteral methods.

As mentioned above, the imaging agent bound to selectins (present eitherin a biological system or in a patient) is detected using an imagingtechnique such as contrast-enhanced ultrasonography, planarscintigraphy, SPECT, MRI, fluorescence spectroscopy, or a combinationthereof.

The methods of the invention that provide for detecting the presence ofselectins in a patient or in a biological system obtained from a patientcan be used to diagnose a pathological condition associated withselectins. The diagnosis can be achieved by examining and imaging partsof or the whole body of the patient or by examining and imaging abiological system (such as one or more samples of biological fluid orbiological tissue) obtained from the patient. One or the other method,or a combination of both, will be selected depending of the clinicalcondition suspected to affect the patient. Comparison of the resultsobtained from the patient with data from studies of clinically healthyindividuals will allow determination and confirmation of the diagnosis.

These methods can also be used to follow the progression of apathological condition associated with selectins. For example, this canbe achieved by repeating the method over a period of time in order toestablish a time course for the presence, localization, distribution,and quantification of “abnormal” selectins in a patient.

These methods can also be used to monitor the response of a patient to atreatment for a pathological condition associated with selectins. Forexample, an image of part of the patient's body that contains “abnormal”selectins (or an image of part of a biological system originating fromthe patient and containing “abnormal” selectins) is generated before andafter submitting the patient to a treatment. Comparison of the “before”and “after” images allows the response of the patient to that particulartreatment to be monitored.

Pathological conditions that may be diagnosed, or whose progression canbe followed using the inventive methods provided herein may be anydisease and disorder known to be associated with selectins, i.e., anycondition that is characterized by undesirable or abnormal interactionsmediated by selectins. Examples of such conditions that mayadvantageously be diagnosed using methods provided herein include, butare not limited, thrombosis, myocardial ischemia/reperfusion injury,stroke and ischemic brain trauma, neurodegenerative disorders, tumormetastasis and tumor growth, and rheumatoid arthritis.

The present Applicants have shown that the selectin-targetedUSPIO-fucoidan nanoparticles that they developed were able to detectintravascular thrombus as small as 100 μm. Consequently, theUSPIO-fucoidan nanoparticles according to the invention may be used inthe early detection of vulnerable plaques, in particular in at riskatherothrombotic patients. Risks factors of atherothrombotic diseaseinclude for example age, gender, family history, cigarette smokinghistory, hypertension, diabetes, cholesterol, obesity, and physicalinactivity.

III—Pharmaceutical Compositions

In the methods of detection/imaging of selectins and of diagnosis ofpathological conditions associated with selectins described herein, theimaging agents of the present invention may be used per se or as apharmaceutical composition. Accordingly, in one aspect, the presentinvention provides for the use of fucoidan for the manufacture of acomposition for the diagnosis of clinical conditions associated withselectins. In a related aspect, the present invention providespharmaceutical compositions comprising at least one selectin-targetedimaging agent of the invention (or any physiologically tolerable saltthereof), and at least one pharmaceutically acceptable carrier.

The specific formulation will depend upon the selected route ofadministration. Depending on the particular type of pathologicalcondition suspected to affect the patient and the body site to beexamined, the imaging agent may be administered locally or systemically,delivered orally (as solids, solutions or suspensions) or by injection(for example, intravenously, intraarterially, intrathecally (i.e., viathe spinal fluid), intradermally or intracavitory).

Often, pharmaceutical compositions will be administered by injection.For administration by injection, pharmaceutical compositions of imagingagents may be formulated as sterile aqueous or non-aqueous solutions oralternatively as sterile powders for the extemporaneous preparation ofsterile injectable solutions. Such pharmaceutical compositions should bestable under the conditions of manufacture and storage, and must bepreserved against the contaminating action of microorganisms such asbacteria and fungi.

Pharmaceutically acceptable carriers for administration by injection aresolvents or dispersion media such as aqueous solutions (e.g., Hank'ssolution, alcoholic/aqueous solutions, or saline solutions), andnon-aqueous carriers (e.g., propylene glycol, polyethylene glycol,vegetable oil and injectable organic esters such as ethyl oleate).Injectable pharmaceutical compositions may also contain parenteralvehicles (such as sodium chloride and Ringer's dextrose), and/orintravenous vehicles (such as fluid and nutrient replenishers); as wellas other conventional, pharmaceutically acceptable, non-toxic excipientsand additives including salts, buffers, and preservatives such asantibacterial and antifungal agents (e.g., parabens, chlorobutanol,phenol, sorbic acid, thirmerosal, and the like). Prolonged absorption ofthe injectable compositions can be brought about by adding agents thatcan delay absorption (e.g., aluminum monostearate and gelatin). The pHand concentration of the various components can readily be determined bythose skilled in the art.

Sterile injectable solutions are prepared by incorporating the activecompound(s) and other ingredients in the required amount of anappropriate solvent, and then by sterilizing the resulting mixture, forexample, by filtration or irradiation. The methods of manufacture ofsterile powders for the preparation of sterile injectable solutionsinclude vacuum drying and freeze-drying techniques.

In general, the dosage of a selectin-targeted imaging agent (orpharmaceutical composition thereof) will vary depending onconsiderations such as age, sex and weight of the patient, as well asthe particular pathological condition suspected to affect the patient,the extent of the disease, the area(s) of the body to be examined, andthe sensitivity of the detectable moiety. Factors such ascontraindications, therapies, and other variables are also to be takeninto account to adjust the dosage of imaging agent to be administered.This, however, can be readily achieved by a trained physician.

In general, a suitable daily dose of a selectin-targeted imaging agent(or pharmaceutical composition thereof) corresponds to the lowest amountof imaging agent (or pharmaceutical composition) that is sufficient toallow detection/imaging of any relevant (i.e., generally overexpressed)selectin present in the patient. To minimize this dose, it is preferredthat administration be intravenous, intramuscular, intraperitoneal orsubcutaneous, and preferably proximal to the site to be examined. Forexample, intravenous administration is appropriate for imaging thecardio/neurovascular system; while intraspinal administration is bettersuited for imaging of the brain and central nervous system.

IV—Kits

In another aspect, the present invention provides kits comprisingmaterials useful for carrying out the diagnostic methods of theinvention. The diagnostic procedures described herein may be performedby clinical laboratories, experimental laboratories, or practitioners.

In certain embodiments, an inventive kit comprises at least one fucoidanand at least one detectable entity, and, optionally, instructions forassociating the fucoidan and detectable entity to form aselectin-targeted imaging agent according to the invention. Thedetectable entity is preferably a short-lived radionuclide such astechnetium-99m (^(99m)Tc), gallium-67 (⁶⁷Ga), yttrium-91 (⁹¹Y),indium-111 (¹¹¹In), rhenium-186 (¹⁸⁶Re), and thallium-201 (²⁰¹T1).Preferably, the fucoidan and detectable entity are present, in the kit,in amounts that are sufficient to prepare a quantity of imaging agentthat is suitable for the detection of selectins and diagnosis of aparticular clinical condition in a subject.

In other embodiments, an inventive kit comprises at least oneselectin-targeted imaging agent according to the invention. In suchembodiments, the selectin-targeted imaging agent is preferablychemically stable.

A kit according to the present invention may further comprise one ormore of: labeling buffer and/or reagent; purification buffer, reagentand/or means; injection medium and/or reagents. Protocols for usingthese buffers, reagents and means for performing different steps of thepreparation procedure and/or administration may be included in the kit.

The different components included in an inventive kit may be supplied ina solid (e.g., lyophilized) or liquid form. The kits of the presentinvention may optionally comprise different containers (e.g., vial,ampoule, test tube, flask or bottle) for each individual component. Eachcomponent will generally be suitable as aliquoted in its respectivecontainer or provided in a concentrated form. Other containers suitablefor conducting certain steps of the preparation methods may also beprovided. The individual containers of the kit are preferably maintainedin close confinement for commercial sale.

In certain embodiments, a kit further comprises instructions for usingits components for the diagnosis of clinical conditions associated withselectins according to a method of the present invention. Instructionsfor using the kit according to a method of the invention may compriseinstructions for preparing an imaging agent from the fucoidan anddetectable moiety, instructions concerning dosage and mode ofadministration of the imaging agent, instructions for performing thedetection of selectins, and/or instructions for interpreting the resultsobtained. A kit may also contain a notice in the form prescribed by agovernmental agency regulating the manufacture, use or sale ofpharmaceuticals or biological products.

EXAMPLES

The following examples describe some of the preferred modes of makingand practicing the present invention. However, it should be understoodthat the examples are for illustrative purposes only and are not meantto limit the scope of the invention. Furthermore, unless the descriptionin an Example is presented in the past tense, the text, like the rest ofthe specification, is not intended to suggest that experiments wereactually performed or data were actually obtained.

Some of the results reported below were presented in scientific articles(L. Bachelet et al., Biochim. Biophys. Acta, 2009, 1790: 141-146; Rouzetet al., J. Nucl. Med., 2011, 52: 1433-1440), which are incorporatedherein by reference in their entirety. Other results reported below werepresented at the International Carbohydrate Symposium, Oslo, Norway,Jul. 24-Aug. 1, 2008 (L. Bachelet et al., “Fucoidan: A sulfatedpolysaccharide to target activated platelets in atherosclerosis”).

Example 1 LMW Fucoidans are Highly Specific Ligands of P-SelectinMaterials and Methods

Chemical Products. Fluorescein isothiocyanate (FITC) was purchased fromFluka (Saint-Quentin Fallavier, France); streptavidin-peroxidaseconjugate from Dako (Trappes, France); diaminopropane, sodiumcyanobromohydride and peroxidase substrate ABTS from Sigma-Aldrich(Saint-Quentin Fallavier, France); sinapinic acid solution from Bio-RadLaboratories (Hercules, Calif., USA); and the amine coupling kit andrunning buffer from BIAcore (Uppsala, Sweden).

Polysaccharides. The low molecular weight fucoidan (based on sulfatedrepeating fucose unit; M=7200 g/M; SO₄=30% (w/w)) was prepared frombrown seaweed as previously described (A. Nardella et al., Carbohydr.Res., 1996, 289: 201-208). The low molecular weight heparin (M=5700 g/M;SO₄=45% (w/w)) and low molecular weight dextran sulfate (M=8000 g/M;SO₄=52% (w/w)), were supplied from Sigma-Aldrich; and the biotinylatedpolyacrylamide-type glycoconjugate containing 20% mol SLe^(x) wasobtained from Lectinity Holding (Moscow, Russia).

Biological Compounds. Recombinant human P-selectin (121-124 kDa bySDS-PAGE) and recombinant human P-selectin/Fc chimera (146-160 kDa bySDS-PAGE) were obtained from R&D Systems (Lille, France); bovine serumalbumin (BSA), thrombin receptor-activating peptide (TRAP), andadenosine diphosphate (ADP) from Sigma-Aldrich, and purified peptide andprotein standards from Bio-Rad Laboratories.

Antibodies. The PC5-labeled IgG (MOPC-21 clone), PC5-labeled antihumanP-selectin (CD62P, AK-4 clone), FITC-labeled IgM and FITC-labeled PAC-1(directed to active conformation of integrin complex GPIIb/IIIa) weresupplied from BD Biosciences (Le Pont de Claix, France); FITC-labeledIgG (MOPC-21 clone), FITC-labeled anti-human CD41 (integrin GPIIb) andgoat anti-human Fc IgGperoxidase from Beckman-Coulter (Roissy, France);goat anti-human Fc IgG from Sigma-Aldrich; anti-human P-selectin (CD62P,G1 clone) from COGER (Paris, France).

Other Materials. Immulon 1B microtiter plates were a gift from VWR(Fontenay sous Bois, France). Anionic protein chips CM10 were obtainedfrom Bio-Rad Laboratories; CM5 sensor chips from BIAcore.

FITC Labeling of Polysaccharides. Five hundred (500) mg ofpolysaccharide and 250 mg of NaBH₃CN were added to 4 mL ofdiaminopropane hydrochloride solution at 2.5 M. After 24 hours at 60°C., 250 mg of NaBH₃CN were added to the mixture and the reaction wascarried on for 48 hours. Samples were dialyzed (cut-off 1000 Da) beforefreezedrying. One hundred and fifty (150) mg of aminated polysaccharidewas dissolved in 6 mL of 0.5 M carbonate buffer (pH 9.6). Six (6) mg ofFITC was added to the solution which was stirred at 4° C. in darknessfor 2 hours. After neutralization, the solution was dialyzed (cut-off1000 Da) and freeze-dried. The colored compound was then dissolved at150 mg/mL in NaCl 1 M, precipitated by ethanol and centrifuged at 4500rpm for 20 minutes to remove the free fluorescein. Fucoidan wassuccessfully fluorolabeled using this protocol with a grafting of0.19±0.06 fluorophore per polysaccharide chain.

P-Selectin Binding Assay with Sialyl Lewis X. This protocol was adaptedfrom a previously described method (Weitz-Schmidt et al., Anal.Biochem., 1999, 273: 81-88). P-selectin/Fc chimera (5 μg/mL in phosphatebuffered saline, PBS, 137 mM NaCl, 8.1 mM Na₂HPO₄, 1.4 mM KH₂PO₄ and 2.7mM KCl, pH=7.2) was coated onto microtiter plates overnight at 4° C. Theplates were washed with the assay buffer (20 mM Hepes, pH 7.4,containing 150 mM NaCl and 1 mM CaCl₂), blocked for 4 hours at 4° C.with 3% BSA in the same buffer, and washed again. Polysaccharides oranti-human P-selectin (G1 clone) and biotinylated SLe^(x)-polymer werediluted in the assay buffer and added to the P-selectin-coated wells orthe BSA-coated wells (non specific control) for incubation overnight at4° C. The plates were then washed and streptavidin-peroxidase diluted1:1000 in the assay buffer was added to the wells. After 4 hours at 4°C., the plates were washed with assay buffer. ABTS peroxidase substratesolution was added and the color reaction was stopped after 10 minuteswith 2% oxalic acid. Bound SLe^(x)-polymer was determined by measuringthe optical density at 405 nm using a microplate reader.

P-Selectin Binding Assay with PSGL-1. P-selectin (5 μμ/mL in PBS, 137 mMNaCl, 8.1 mM Na₂HPO₄, 1.4 mM KH₂PO₄ and 2.7 mM KCl, pH=7.2) was coatedonto microtiter plates overnight at 4° C. The plates were washed withthe assay buffer (20 mM Hepes, pH 7.4, containing 150 mM NaCl and 1 mMCaCl₂), blocked for 4 hours at 4° C. with 3% BSA in the same buffer, andwashed again. Fucoidan and PSGL-1/Fc chimera were diluted in the assaybuffer and added to the P-selectin-coated wells or the BSA-coated wells(non specific control) for incubation overnight at 4° C. The plates werethen washed and IgG antiFc-peroxidase diluted 1:1000 in the assay bufferwas added to the wells. After 4 hours at 4° C., the plates were washedwith the assay buffer. ABTS peroxidase substrate solution was added andthe color reaction was stopped after 5 minutes with 2% oxalic acid.Bound PSGL-1 was determined by measuring the optical density at 405 nmusing a microplate reader.

SELDI-TOF Analysis. Anionic protein chip arrays CM10 were employed.Spots were prewetted twice for 5 minutes with 5 μL of Hepes pH 7.0.Samples were prepared by mixing 500 ng of recombinant human P-selectinin the absence or in the presence of different concentrations ofpolysaccharides (molar ratio between P-selectin and polysaccharide of 1per 1 to 1 per 100), diluted in 1 M Hepes pH 7.0, in a total volume of 5μL, and incubated for 1 hour at 4° C. The samples were applied to thespots and incubated for 45 minutes at room temperature in a humidchamber. The spots were washed three times with 5 μL of 1 M Hepes pH 7.0and twice with 5 μL of distilled water and then air-dried for 10minutes. One (1) μL of a saturated solution of sinapinic acid (in 50%acetonitrile, 0.5% trifluoroacetic acid) was applied twice to each spot.The protein chip arrays were analyzed using a protein chip reader (PBSII, Bio-Rad). The protein masses were calibrated externally usingpurified peptide and protein standards. Spectra were analyzed withprotein chip software 3.1.1 (Bio-Rad).

Surface Plasmon Resonance. BIAcore 2000 optical biosensor was used. Thecarboxymethylated dextran surface CM5 sensor chip was coupled with goatanti-human Fc IgG using standard amine coupling chemistry (averaged 6500RU). Recombinant human P-selectin/Fc chimera was then captured to thechip (averaged 1750 RU). Goat anti-human Fc IgG was used as non specificcontrol. Samples were diluted in running buffer (10 mM Hepes, 150 mMNaCl, 1 mM CaCl₂, and 0.005% Tween-20, pH 7.4). Flow cell, temperature,flowrate, sample volume, and mixing were selected using the BIAcorecontrol software. Sensorgrams were analyzed using the BIAevaluationsoftware.

Flow Cytometry. Blood from healthy adult donors was collected intosodium citrate 3.8% (w/v). Citrated human whole blood (5 μL) was dilutedto 40 μL with PBS (137 mM NaCl, 8.1 mM Na₂HPO₄, 1.4 mM KH₂PO₄ and 2.7 mMKC1, pH=7.2). Platelets were activated by adding ADP at a finalconcentration of 2.5 μM or TRAP at a final concentration of 200 μM. FiveμL of LMW polysaccharides (FITC-labeled or not, diluted in PBS) and 5 μLof fluorolabeled antibody (PC5-labeled antiCD62P AK-4 clone orFITC-labeled PAC-1 or FITC-labeled antiCD41; diluted 8:100; 5:100 and3:100 in PBS) were added at room temperature for 20 minutes. Thesolutions were diluted to 1 mL with PBS before analysis by flowcytometry. Data were collected on a Coulter EPICS XL-MCL flow cytometer(Beckman Coulter). Samples analysis was performed on side and forwardscatter, and fluorescence was acquired in FL1 (fluorescein) or FL4 (PC5)using the logarithmic mode. 7500 events were collected from each sample.The level of platelet activation was assessed by the positivity of theanti-Pselectin (CD62P, AK-4 clone) antibody (0.4%, 73.4%, and 97.8% fornon-activated, ADP-activated and TRAP-activated platelets,respectively). Data were processed using GEN S® System II software(Beckman Coulter) and histograms are presented overlapped for thedifferent conditions.

Statistical Analysis. Data shown are representative results of at leastthree identical and independent experiments carried out each time withn≧3 samples per conditions. Statistical comparisons were performed withthe Student's t-test.

Results

LMW fucoidan inhibits the binding of SLe^(x) and PSGL-1 to P-selectin.The binding of SLe^(x)-polyacrylamide-biotin to immobilized P-selectinwas measured in the presence of LMW fucoidan, heparin and dextransulfate. In this assay, an anti-human P-selectin antibody (clone G1, asa positive control) completely blocked the binding of SLe^(x) toP-selectin. The amount of SLe^(x) bound to P-selectin decreased withincreasing concentrations of polysaccharides. However, major differenceswere observed between the sulfated polysaccharides (FIG. 1). Inhibitionby fucoidan was much more pronounced than with heparin and dextransulfate, with an IC₅₀ of 20 nM, 400 nM and >25,000 nM, respectively. Thebinding of PSGL-1/Fc chimera to immobilized P-selectin was alsoevaluated in the presence of LMW fucoidan. The amount of PSGL-1 bound toP-selectin decreased with increasing concentration of fucoidan with anIC₅₀ of 5 nM.

Binding of LMW fucoidan to P-selectin. The binding of P-selectin wasthen analyzed by mass spectrometry and by surface plasmon resonance(SPR). The formation of a complex between P-selectin and the three LMWsulfated polysaccharides and native dextran was analyzed using SELDI-TOFMS. Anionic chips on which P-selectin bound (isoelectric point ˜6.5) atphysiological pH=7 were used. P-selectin was then desorbed by laser anddetected as a SELDI-TOF broad peal of ˜100 kDa. The amount of P-selectinmarkedly decreased the presence of LMW fucoidan, and in a dose-dependentmanner. P-selectin retention to the chip also decreased with heparin butwas not affected by incubation with native dextran or dextran sulfate.These results demonstrate that LMW fucoidan forms a complex withP-selectin in solution thus preventing its retention to the anionicsurface.

The binding characteristics of LMW sulfated polysaccharides toP-selectin were further compared using surface plasmon resonanceanalysis. LMW fucoidan, heparin and dextran sulfate were flowed on asensorchip coated either with anti-human Fc IgG or with recombinanthuman P-selectin/Fc chimera (FIG. 2). All polysaccharides bound toP-selectin and, to a lesser extent, to anti-human Fc IgG used as acontrol. The signal difference obtained on P-selectin vs IgG was higherwith fucoidan than with heparin or dextran sulfate, which suggests thatfucoidan exhibits a better selectivity (FIG. 2A). Dissociation constantsof LMW fucoidan, heparin and dextran sulfate for P-selectin, calculatedusing a 1:1 Langmuir binding model (FIG. 2D), were found to be 1.2 nM,577 nM and 118 nM, respectively. These results confirmed that LMWfucoidan has an affinity for P-selectin at least two orders of magnitudehigher than the two other polysaccharides.

Binding of LMW Fucoidan to Human Platelets. Heparin was previouslyreported to bind to platelets (J. Hirsh et al., Chest, 2004, 126:188S-203S; R. Verhaege, Acta Cardiol., 1998, 53: 15-21). Flow cytometryexperiments were performed by incubating human citrated whole blood withFITC-labeled LMW fucoidan. A representative experiment is reported onFIG. 3. Platelets were gated on side and forward scatter and theirpositivity for a fluorolabeled specific platelet antibody (CD41).FITC-labeled fucoidan bound to activated platelets as demonstrated by ashift of the fluorescence to the right. Fucoidan binding increased withthe level of platelet activation as indicated by the percentage ofpositive platelets, 34.7%, 51.4%, and 69.1% for nonactivated,ADP-activated and TRAP-activated platelets, respectively.

TRAP-activated platelets were then incubated with a fluorolabeledanti-CD62P antibody in whole blood in the presence or in the absence ofnon-fluorolabeled LMW fucoidan. Inhibition of the CD62P antibody bindingto activated platelets was observed in the presence of LMW fucoidan asindicated by a decrease in the mean fluorescence intensity (FIG. 4). Inaddition, LMW fucoidan did not inhibit the binding of CD41 (integrinGPIIb) antibody or PAC-1 (directed to the active conformation of theintegrin complex GPIIb/IIIa) to activated platelets, indicating that itseffect on CD62P antibody binding to activated platelets was specific.Taken together, these results indicate that the binding of LMW fucoidanto activated platelets observed in whole human blood was mediated byP-selectin.

Discussion

Sulfated carbohydrates are known to have a wide variety of biologicalactivities (S. Soeda et al., Biochim. Biophys. Acta, 2000, 1497:127-137). Sulfated polysaccharides have previously been described asP-selectin ligands (A. Varki et al., PNAS, 1994, 91: 7390-7397; D.Simonis et al., Biochemistry, 2007, 46: 6156-6164) e.g., heparin andmodified heparins (A. Koenig et al., J. Clin. Invest., 1998, 101:877-889), high molecular weight fucoidan and dextran sulphate (M. P.Skinner et al., J. Biol. Chem., 1991, 266: 5371-5374). In the presentstudy, the interaction of three low molecular weight sulfatedpolysaccharides (fucoidan, heparin and dextran sulfate) with P-selectinwas characterized using four different methods. LMW fucoidan is apromising candidate for the treatment of inflammation disorders (K.Senni et al., Arch. Biochem. Biophys., 2006, 445: 56-64) andcardiovascular diseases (33; 34; F. Zemani et al., Arterioscler. Thromb.Vasc. Biol., 2008, 28: 644-650). LMW heparin is used in the treatment ofthrombotic disorders (K. A. Fox et al., Eur. Heart J., 2000, 21:1440-1449). Synthetic dextran sulfate and mimetics were alsoinvestigated as putative drugs in various diseases, including infectiondiseases (J. Neyts et al., Biochem. Pharmacol., 1995, 50: 743-751).

The inhibition of SLe^(x)/P-selectin binding was quantified in bindingassay experiments ranking polysaccharides as follows (IC₅₀): fucoidan(20 nM)>heparin (400 nM)>dextran sulfate (25,000 nM). As a comparison,Koenig et al. established by inhibition assays that heparin inhibitedP-selectin binding to Sialyl Lewis X with IC₅₀ between 82 and 2400 μMdepending on the size of the heparin fragment (A. Koenig et al., J.Clin. Invest., 1998, 101: 877-889). However, in their work, Sialyl LewisX was immobilized whereas, in the present approach, it is P-selectinthat was immobilized. The functional importance of LMW fucoidan bindingto P-selectin was evidenced by the interference in the interactionbetween the glycoprotein with its natural ligand PSGL-1.

SELDI-TOF mass spectrometry was used to highlight the formation of acomplex between P-selectin and LMW polysaccharides. This tool hasallowed to demonstrate the binding of heparin and fucoidan to thrombinand protease nexin-I (B. Richard et al., Thromb. Haemost., 2006, 95:229-235). SELDI-TOF MS experiments showed that, in solution, LMWfucoidan formed a complex with P-selectin at physiological pH in adose-dependent manner. The complex formation decreased P-selectinretention to an anionic surface.

The interaction of sulfated polysaccharides such as heparin or fucoidanwith various proteins has been previously studied by surface plasmonresonance (BIAcore®) (32; H. Yu et al., Biochim. Biophys. Acta, 2005,1726: 168-176). For instance, it was shown that a SLe^(x) mimetic bindsto P-selectin with K_(D) of 114 μM (M. E. Beauharnois et al.,Biochemistry, 2005, 44: 9507-9519) and PSGL-1 binds to P-selectin withK_(D) of 320 nM (P. Mehta et al., J. Biol. Chem., 1998, 273:32506-32513). The dissociation constant of LMW heparin for P-selectincalculated here, with a K_(D) above 500 nM, is in the same range asthose of three unfractioned heparins determined by quartz crystalmicrobalance measurements in the study of Simonis et al. (Biochemistry,2007, 46: 6156-6164). Interestingly, this results demonstrated that LMWfucoidan with a K_(D) in the nanomolar range is the most effective andselective P-selectin ligand when compared with other LMWpolysaccharides, PSGL-1 and the SLe^(x) mimetic. Moreover,P-selectin/LMW fucoidan interaction is stronger than theL-selectin/GlyCAM-1 interaction, also involved in leukocyte rolling onblood vessels endothelium. The interaction constant of this interactionwas determined to be 108 μM by Nicholson et al. (J. Biol. Chem., 1998,273: 763-770).

Native and fractionated heparins were shown to interact with P-selectinon HL-60 cells (Y. Gao et al., Mol. Cells, 2005, 19: 350-355). In orderto determine whether the binding of fucoidan to P-selectin observedusing purified proteins could occur in more complex conditions, theinteraction of LMW polysaccharides with human platelets on whole bloodwas analyzed. Using flow cytometry, LMW fucoidan was found to bind toactivated platelets and the level of binding was found to correlate withthe degree of platelet activation. Moreover, LMW fucoidan was able toinhibit the binding of an anti P-selectin antibody to activated humanplatelets.

Example 2 ^(99m)Tc-labelled Fucoidan as P-selectin-targeted ImagingAgent for the in vivo Scintigraphic Detection of Platelet Activation andAccumulation

Fucoidan was labelled with technetium-99m (^(99m)Tc) using thewell-known stannous reaction in solution. Briefly, 4 μL of stannouschloride were added to 10 μL of fucoidan (1 mg/mL, MW=7200) followed by2 μL of potassium borohydride. Immediately after combination of thesereagents, 50 μL of ^(99m)Tc (corresponding to 15-30 mCi) were gentlyadded to the mixture. The labelling reaction was complete after 1 hourof incubation. Control of the labelling was performed using thin layerpaper chromatography and methyl-ketone as eluant. The percentage oflabelling was 100%.

Rat models of endocarditic vegetations, aneurysmal and atrial trombiwere used as animal models of clinical conditions associated withplatelet activation and fibrin formation. Intravenous injection of 1 μgof ^(99m)Tc-labelled fucoidan allowed the in vivo visualization ofplatelet-rich endocarditic vegetations (FIG. 5), atrial (FIG. 6) andaneurysmal thrombi (FIG. 7). These in vivo data were confirmed by exvivo autoradiography showing the exact histological co-localization ofthe signal with valves vegetations or thrombus with a very highquantitative signal to background ratio of 8 to 10.

The development of fucoidan as a radiotracer for selectin imaging can beconsidered at several steps: (1) ability to visualize P-selectinoverexpression by acutely-activated endothelium (ischemia-reperfusionmodel); (2) ability to visualize E-selectin overexpression bychronically-stimulated endothelium (L-NAME model of hypertension); and(3) ability or not to visualize L-selectin accumulation in tertiarylymph node formation (aortic allograft in rats) and in auto-immunemyocarditis.

Example 3 Preparation of fucoidan-coated USPIO Particles

The present Applicants have developed five different strategies to coatfucoidan onto USPIO particles.

The first strategy involves the synthesis of iron particles in thepresence of unmodified fucoidan. The Applicants have applied a method ofsynthesis previously described with dextran (R. S. Molday et al., J.Immunol. Methods, 1982, 52: 353-367) replacing dextran MW 40000 byfucoidan MW 50500. Fucoidan-coated iron nanoparticles were obtained.However, these particles were found to be unstable in water.

The second strategy comprises the coating of an acidic ferrofluid withunmodified fucoidan. Fucoidan was incubated with acidic ferrofluid.Fucoidan-coated iron nanoparticles were obtained that were stable inaqueous medium pH 7.4, but unstable in buffers with ionic strength of0.15 M, which are used in most applications. The synthesis could beobtained in the presence of a cross-linker (A. San Juan et al., J.Biomed. Mater Res. A, 2007, 82: 354-362) to increase the stability ofthe nanoparticles.

Three other strategies have been developed that are based on thegrafting of fucoidan to maghemite γFe₂O₃ nanoparticles via a linker(strategy 3), or the coupling of fucoidan to dextan-coated maghemiteγFe₂O₃ nanoparticles, i.e., coated with carboxymethyl dextran or CMD(strategy 4) or coated with oxidised dextran (strategy 5). In all thesestrategies, the first step is to functionalize the reducing end offucoidan with a primary amine to allow subsequent reaction withoutaltering the fucoidan chain structure and therefore its affinity forP-selectin.

In strategy 3, the iron nanoparticles were thiolated withdimercaptosuccinic acid (DMSA) as previously described (French patentNo. 2 736 197; N. Fauconnier et al., J. Colloid Interface Sci., 1997,194: 427-433), and then linked to the aminated fucoidan by a disulfidebridge using a heterobifunctional linker, N-succinimidyl3-(2-pyridyldithio) propionate (SPDP) (J. Roger et al., Eur. Phys. J.Applied Phys., 1999, 5: 321-325). Iron nanoparticles coated with a LMWfucoidan (MW=7200) were obtained that were found to be stable in usualaqueous buffer pH 7.4 with ionic strength of 0.15 M.

In strategy 4, CMD (MW=15000) was incubated with acidic ferrofluid toobtain CMD-coated iron nanoparticles stable in usual aqueous buffer pH7.4 with ionic strength of 0.15 M. Aminated fucoidan is grafted on thesenanoparticles using standard amine coupling chemistry (with EDC/NHSsystem).

In strategy 5, aminated fucoidan is grafted to oxidized dextran-coatednanoparticles by formation of Schiff bases.

Example 4 Fucoidan-coated Acoustically Active Microbubbles and Liposomes

Several strategies are investigated to graft fucoidan onultrasound-based imaging contrast agents. In a first approach, aminatedfucoidan is grafted to phospholipids-based, perfluorobutane-filledmicrobubbles using standard amine coupling chemistry as previouslydescribed by Villanueva et al. (Circulation, 1998, 98: 1-5). Briefly,perfluorobutane was dispersed by sonication in aqueous medium containingphosphatidylcholine, a surfactant, a phosphatidylethanolamine derivativeand a phospholipid derivative containing carboxyl groups which wereactivated with 1-ethyl-3(3-dimethylaminopropyl) carbodiimide (EDC) andaminated fucoidan was then covalently attached via primary amino groupswith the formation of amine bonds.

A second strategy is to graft biotinylated fucoidan tophospholipid-based, perfluorobutane-filled microbubbles via a multi-stepavidin/biotin bridging chemistry as previously described by Weller etal. (Biotechnol. Bioeng., 2005, 92: 780-788). Briefly, an aqueous salinesolution containing phosphatidylcholine, polyethylene glycol stearateand a biotinylated derivative of phosphatidylethanolamine was sonicatedwith perfluorobutane. The microbubbles formed were incubated withstreptavidin, and then a saturating amount of biotinylated fucoidan.

Biotinylated fucoidan was obtained using a method previously describedby Osmond et al. (Anal. Biochem., 202, 310(2), 199-207) for thebiotinylation of an aminated heparin. Briefly,sulfosuccinimidyl-6-(biotinamido)hexanoate-(sulfo-NHS-LC-biotin) wasadded to a solution of aminated fucoidan in carbonate buffer 0.1 M pH=8with a molar ratio between aminated fucoidan and sulfo-NHS-LC-biotin of1 to 10. The mixture was vortexed and shaken overnight at 4° C., and wasthen dialyzed (cut-off 1000 Da) against bi-distilled water beforefreeze-drying.

Finally, a third approach is to graft fucoidan to acoustically activeliposomes using a thiol chemistry as previously described by Hamilton etal. (Circulation, 2002, 105: 2772-2778). Briefly, componentphospholipids (phosphatidylcholine, phosphatidyl-glycerol,phosphatidylethanolamine derivative and cholesterol) were dissolved inchloroform and mixed and the resulting film was sonicated in water toform liposomes; aminated fucoidan was reacted with3-(2-pyridylthio)propionic acid-N-hydroxysuccinimide ester (SPDP). Thefucoidan derivative was then reduced in dithiothreitol solution and thethiolated fucoidan was then conjugated to liposomes.

Example 5 Fucoidan Substituted with Iodinated Tyrosine for X-rayRadiography

Another possibility for the radiolabelling of fudoidan is the use ofsodium iodide after grafting of a tyrosine residue onto the reductiveend of the polysaccharide. The substitution step is similar to theamination step described in Example 1.

Briefly, 200 mg of polysaccharide and 100 mg of NaBH₃CN were added to1.6 mL of a tyrosine hydrochloride solution at 2.5 M. After 24 hours at60° C., 100 mg of NaBH₃CN were added to the mixture and the reaction wasprolonged for 48 hours. The sample was dialyzed (cut-off 1000 Da)against bidistilled water before freeze-drying. Modified fucoidan wasrecovered in a 50-70% yield with a grafting of 0.50±0.05 of tyrosine perpolysaccharide chain.

Iodination was performed using chloramine-T as follows: 20 μmoles ofmodified fucoidan (14.5 mg) in 450 μL of phosphate buffer saline 0.05 M,pH 7.4 (PBS) were added to a NaI solution (150 μL of 8% w/v solution inPBS) followed by the addition of 350 μL of a chloramine-T solution (40mg/mL in PBS). The mixture was vortexed, and shaken overnight at 4° C.The reaction mixture was then dialyzed against bidistilled water (cutoff 1000 Da) and freeze-dried to get the iodinated modified fucoidan inquantitative yield.

Example 6 In vivo P-Selectin Targeted Molecular Imaging of IntraLuminalThrombus by MRI using USPIO-Fucoidan in Experimental Abdominal AoarticAneurysms

The Applicants have developed a novel approach to P-selectin molecularimaging using fucoidan, as pharmacophore, conjugated to neutralpolysaccharide-enrobed nanoparticles of iron oxide (i.e., ultra smallsuperparamagnetic iron-oxides, USPIOs), as contrastophore. The abilityof this new contrast agent to detect active intravascular thrombusfollowing elastase vascular injury was evaluated in vivo in anexperimental model in rats (Anidjar et al., Circulation, 1990, 82:973-981).

Materials and Methods

Contrast Agents. USPIO coated with carbodymethyldextran (USPIO-CMD) andUSPIO coated with fucoidan (USPIO-FUCO) were prepared as describedbelow. The depolymerized fucoidan used, which was obtained from Algueset Mer (Ouessant, France), had a molecular weight of 7200 g/mol. Afterrefinement of USPIO-FUCO and USPIO-CMD, the iron concentration of eachcontrast agent was adjusted to 25 mM.

Coating of Acidic Ferrofluide with CMD-Fucoidan. The startingferrofluide was synthesized using a classical method (Rivière et al.,Radiology, 2005, 235: 959-967), and kept in acid ([Fe]=1.05 M). In afirst step, the coating of acidic carboxymethyldextran (CMD, M=15000g/mol, [COOH]=1.3 mmol/g, Sigma Aldrich) was performed according to themethod described by Roger el al. (Eur. Phys. J. Applied Phys., 1999, 5:321-325). A sample of 5 mL of USPIO-CMD ([Fe]=0.05 M) was treated with20 mg of EDC and 3.0 mg of NHS for 15 minutes at room temperature.Fucoidan, which had previously been aminated at its reducing end usingdiaminopropane (Kondo et al., Agric. Biol. Chem., 1990, 54: 2169-2170;Seo et al., Bioconjug. Chem., 2007, 18: 2197-2201), was added to thereaction mixture ([fucoidan]=15 mg/ml) and the resulting mixture wasmaintained under agitation for 2 additional hours. Purification wasperformed by dialyzing the suspension against NaCl 1M (2×) andbidistilled water (5×) before ultrafiltration on MicroSep 100 kDa (Pall,VWR France). Aliquots of 500 μL of USPIO-FUCO ([Fe]=0.05 M) wereprepared in 0.15 NaCl and stored at −80° C. until they were used.Average diameters and zeta potentials of USPIO-FUCO and USPIO-CMD weredetermined using a Zetasizer nano ZS instrument (Malvern Instruments,Orsay, France) and found to be 39.4 nm, −9.0 mV and 65.6 nm, −12.3 mV,respectively.

Relaxation Measurements. For USPIO-CMD and USPIO-FUCO, relaxivitymeasurements were performed at different concentrations of compounds inpure water at 37° C. using relaxometers at 20 MHz (0.47 T, MinispecPC-120, Bruker, Karlsruhe, Germany) and at 60 MHz (1.42 T, Minispecmq-60, Bruker, Karlsruhe, Germany).

Blood Clearance Assessment. In order to determine the biodistribution ofUSPIO-FUCO in vivo, blood clearance of USPIO-FUCO was assessed viaradioactive counting of iterative blood samples. USPIO-FUCO wasradiolabeled according to a classical reducing reaction withpertechnetate (Rouzet et al., J. Nucl. Med., 2011, 52: 1433-1440).Sodium pertechnetat (^(99m)TcO₄ ⁻, about 740 MBq in <100 μL saline,freshly eluted) and 4 μg of stannous chloride (1 μg/μL; Sigma-Aldrich)were added to a vial containing 300 μL of the USPIO-FUCO solution(corresponding to 500 μg of LMW fucoidan), and left to incubate for 1hour at room temperature. Quality control was performed with instantthin-layer chromatography developed in methyl ethyl ketone buffer. Theradiochemical purity was always superior to 99%. For blood clearanceassessment, four male Wistar rats were anesthetized with urethan (1.22g/kg) and a catheter (0.7 mm diameter, Jelco Critikon) was inserted intothe left carotid for sampling. Each animal received a single intravenousinjection (penis vein) of 20 MBq of ^(99m)Tc-USPIO-FUCO in a 250 μLvolume. Blood samples (250 μL) were taken 5, 15, 30, 45, 60, 90, 120,180 and 240 minutes post-injection. Saline (250 μL) was injectedimmediately after each sampling to maintain blood volume and to rinsethe catheter. For each sample, one aliquot of 100 μL was taken for wellcounting (Cobra II, Packard, USA).

Experimental Rat Model. Male Wistar rats (n=28) were purchased from CEJ(Le Genest, France). Twenty-four (24) rats were involved in theelastase-perfused group, and 4 rats were shame-operated forbiodistribution determination. The abdominal aortas of the rats (at 7weeks of age) were perfused with elastase according to a methodpreviously described (Anidjar et al., Circulation, 1990, 82: 973-981).Briefly, under peritoneal pentobarbital anesthesia (4 mg/100 g bodyweight; Ceva Santé Animale), about 15 mm of the infrarenal aorta(beginning 2 mm below the left renal artery) was separated from the venacava. Collateral arteries were exposed from surrounding connectivetissue, and were ligated at two places and cut between them. Abdominalaorta was clamped, and a small hole was made to insert a catheter.Micro-catheter was inserted directly below the cephalad side clamping,and then washed with physiologic saline. A distal thread was tightenedaround the catheter producing a closed perfusion chamber. Four units ofpancreatic porcine elastase (E-1250, Sigma) in 550 μL NaCl 9% wereperfused transmurally for 1 hour, using an automatic pressure perfusionpump. The segment was then rinsed well; flow was re-established, andsurgical wounds were closed (Coutard et al., J. Vasc. Res., 2009, 47:355-366). To localize the treated segment following MRI sessions, at theend of the elastase perfusion, the distance between the upper and lowerpoints of the perfused segment and the left renal artery diameter wasmeasured using a scale within the microscope eyepiece. This model ischaracterized by the constant presence of a more or less important ILT 2weeks after induction (Coutard et al., J. Vasc. Res., 2009, 47:355-366).

The procedure and animal care complied with the “Principles of animalcare” formulated by the European Union (Animal Facility Agreement No.75-18-03, 2005), and animal experimentation was performed underauthorization No. 75-101 of the French Ministry of Agriculture.

In vivo MRI. In vivo MRI experiments were conducted using a 4.7horizontal bore magnet (Bruket BioSpin47/40, Germany) with 20 cm-wideactively shielded gradient coils (100 mT/m). Six days after operation,the rats were anesthetized with pentobarbital and a right jugular venouscatheter was inserted to inject the contrast agent. The animals weredivided into 2 groups: Group 1: injection of USPIO-FUCO; Group 2:injection of USPIO-CMD.

The animals were maintained anesthetized using a 1.5% isoflurane/O₂ gasmixture (100 cc/min maintenance dose) delivered through a nose cone andplaced in a 30 mm birdcage coil with an animal handling system. Toconfirm correct animal position and localize aortic aneurysm, eachanimal was scanned using a phase contrast magnetic resonance angiography(MRA) (parameters: TR/TE=17/5.8 msec; flip angle=20°; ETL=1; slicethickness=10 mm; matrix=256×256; FOV=715×331 mm). Axial slices were thenacquired along the aorta aneurysm before and after (i.e., 2, 15, 30, 45and 60 minutes after) injection of 200 μmol of iron/kg of contrastmaterial using a FSPGR T2*-weighted sequence (fast spoiled gradientecho) (parameters/TR/TE=545.6/6.6 msec; flip angle=60°; ETL=1; slicethickness=1 mm; matrix=384×384; FOV=720×330 mm).

Ex vivo MRI. Two rats with abdominal aneurysm confirmed with FSPGR scanwere used. Under deep anesthesia, left common carotid artery was exposedand secured. A small catheter was retrogradely introduced from themiddle of the left common carotid artery into the aorta. The abdominalaortic aneurysm was dissected free from surrounding inflammatoryadhesions. Using automatic infusion pump, 40 mL of physiologic saline(10 mL/min) were infused using the carotid catheter and washed bycutting the vena cava, followed by infusion of 40 mL of paraformaldehyde(10 mL/min). After sacrifice, the removed aorta was soaked in a tubewith paraformaldehyde for ex vivo imaging.

To confirm the precise distribution of USPIO-FUCO, ex vivo highresolution MRI was performed using a Bruker 7T PharmaScan 70/16 equippedwith a Bruker 98/38 RF Coil, operated using a Paravision softwareplatform (Bruker, Karlsruhe, Germany). A T2*-mapping sequence with thefollowing parameters was used: echo time=3.8, 9.2 and 14.5 ms;repetition time=852.4 ms; flip angle=30 degree; number of average=1;imaging slice thickness=0.125 mm; image matrix=256×256; field ofview=20.141×20 mm; scan time=17 hours and 30 minutes.

Histology. After in vivo MR imaging, the length and the maximum diameter(D_(post)) of the elastase perfused aortic segment were measured using acalibrated grid placed in the dissecting microscope eyepiece. The degreeof aortic dilatation (ΔD%) due to elastase infusion was assessed usingthe following equation:

ΔD(%)=(D _(post) −D _(pre))/D _(pre)×100

where D_(post) is the maximum diameter of the aorta before elastaseinfusion (this diameter was measured during the first surgery). Ratswere then euthanized by intravenous pentobarbital overdose. The portionof aorta with dilatation was removed and flushed with saline. In eachrat, the aorta was cut into 4 equal tissue rings as follows: one cut wasperformed in the center of the tissue sample, another cut, in the centerof each of the two halves. Four 2 mm rings were thus obtained. One upperring and one lower ring were fixed in 10% paraformaldehyde for 24 hoursand the other two rings were frozen at −20° C. The samples fixed inparaformaldehyde were embedded in paraffin, and cut in 5 mm sections formorphological analysis (Masson trichrome) and immunostaining ofP-selectin after antigen retrieval (2 min. ultrasound). A goatanti-mouse P-selectin antibody (SC 6943, Santa Cruz 10 Biotechnology,Santa Cruz, USA) (1/50) was used and was revealed using an anti-goatantibody conjugated to horseradish peroxidise (HRP), followed by areaction in the presence of 3,3-diaminobenzidine (DAB).

The thickness of thrombi in samples stained with trichrome masson stainwas measured by one independent operator using a calibrated grid placedin the optical microscope eyepiece (under a magnification of ×40).

Electron Microscopy. The tissue samples were first washed with PhosphateBuffer Saline solution (PBS), and then fixed with a mixture of 2%Paraformaldehyde (PFA) and 0.3% glutaraldehyde in 0.1M Phosphate Buffer(PB) (pH 7.4) for 2 hours. Then, small pieces of tissue were post-fixedin 1% PFA in 0.1 PB for prolonged time. The samples were rinsed severaltimes in the same buffer, and then post-fixed with 1% osmium tetroxidefor 2 hours. The samples were further rinsed, then progressivelydehydrated using graded ethanol, and finally embedded in Epon 812 resin.Ultra-thin sections were taken, placed on carbon coated copper grids,stained with uranyl acetate and lead citrate, and then examined with aJEOL 2010 high-resolution analytical transmission microscope (HRTEM)operated at 200 keV. A Gatan Imaging Filter 2000 system connected to theTEM was offered access to element maps, using energy filteredtransmission electron microscope (EFTEM). Chemical composition wasestablished using electron energy-loss spectroscopy (EELS).

Quantification of Signal Enhancement on MR Images. All image analysiswas performed using software (OsiriX DICOM reader v3.7, OsiriXFoundation, Geneva, Switzerland). Maximal artifactual luminal magneticsusceptibility artefact into the aortic lumen, was quantified by thepercentage reduction (ΔR%) in aortic luminal area according to a methodpreviously published by the present Applicants (Hyafil et al.,Arterioscler. Thromb. Vasc. Biol., 2006, 26: 176-181).

Analysis of arterial wall contrast agent uptake was performed on the 3slices that anatomically corresponded to sections obtained on histology.On these slices, intra-luminal areas that showed visual intra-luminalsignal drop (ILSD) 1 hour after injection of the contrast agent weremanually contoured for quantitative signal analysis. These regions ofinterest (ROI) were pasted on all corresponding images acquired afterinjection of the contrast agent.

The signal-to-noise ratio (SNR) of aortic wall thrombus was measured bycalculating the average signal intensity (SI) in the ROI from MR imagesat each imaging point (SNR=[SI_(aortic)wall-SI_(muscle)/]SD_(noise signal)). Then, normalized signalenhancement (ΔNSE) was calculated using the following equation:

ΔNSE(%)=(SNR _(t=n) −SNR _(t=before))/SNR _(t=before)×100

where ‘n’ corresponds to the time (in minutes) that separates contrastagent injection and image acquisition (n=2, 15, 30, 45, 60). ΔNSE(%)values for each value of ‘n’ were plotted, and statistical analyses wereperformed (Botnar et al., Circulation, 2004, 110: 1463-1466).

Statistical Analysis. All the statistical analyses were performed usinga computer software (Dr.SPSS II for Windows, SPSS Japan Inc. Tokyo). A1-way ANOVA was carried out to compare the area changes on MRI imagesbetween the different groups. Continuous variables were expressed asmedian and range, and compared using a non-parametric Mann-Whitney Utest. An ANOVA test with repeated measures was used to evaluate thetime-course of USPIO-FUCO. P<0.05 was considered as indicative of asignificant difference between groups.

Results

Relaxivity of the Contrast Agents. The relaxivity of USPIO-CMD and ofUSPIO-FUCO (r1 and r2) was determined in water at 37° C. at 20 MHz and60 MHz. The results obtained are presented in Table 1.

TABLE 1 Relaxivity measurements recorded at 37° C. in water at 20 MHz(0.47 T) and 60 MHz (1.42 T). Contrast agent Frequency (MHz) r₁(mM⁻¹s⁻¹) r₂ (mM⁻¹s⁻¹) USPIO-CMD 20 38.8 ± 1.9 123 ± 6.2 60 15.5 ± 0.7119 ± 5.9 USPIO-FUCO 20 37.5 ± 1.8 137 ± 6.9 60 15.2 ± 0.7 137.4 ± 6.9 

Blood Clearance of ^(99m)Tc-USPIO-FUCO in Normal Rats. After intravenousinjection, ^(99m)Tc-USPIO-FUCO underwent clearance from the bloodaccording to a 2-compartment model. The rapid component (α) accountedfor 70% of the injected activity and had an effective half-life of 9minutes. The slow component (β) accounted for 30% of the injectedactivity and had a much longer effective half-life of 316 minutes. Thus,after a rapid decrease following injection, blood activity reached aplateau after 60 minutes at a mean value of 4.4% of the injected dose[3.1%-5.5%] (FIG. 8).

Anatomical Characteristics of Aneurysms and Wall Thrombus. Four rats (3of which belonged to Group 1 and one of which belonged to Group 2) diedbefore MR imaging. The causes of death included (1) rupture of abdominalaorta (n=2); (2) hindlimb paresis (n=1), and (3) unknown (n=1). Amongthe 20 rats that finished MRI examination, all rats (20/20, 100%) showeddilatation of the injured abdominal aorta (average diameter and standarddeviation of rat's aortas: proximal diameter, 1.85±0.2 mm: distaldiameter, 1.52±0.5 mm: maximal diameter of aneurysmal portion, 5.20±2.1mm: length of aneurysmal portion, 19.2±2.7 mm: degree of aneurysmaldilatation (ΔD%), 319.2±134.9%). No significant differences betweenGroup 1 and Group 2 were observed in terms of ΔD% and aortic diameter,there was no significant difference between Group 1 and Group 2 (p=0.761and p=0.490 respectively).

Mill Intraluminal Signal Drop and Thrombus Identification. In Group 1,all the rats showing thrombus by histology showed a corresponding visualintra-luminal signal drop (ILSD) 1 hour after injection of USPIO-FUCO(FIGS. 9, a and b) and there was no signal drop on healthy parts of theabdominal aorta. In histology, the aortic wall corresponding to the MRIsignal drop was always occupied by an ILT with a more or less circularextension along the aortic wall (FIG. 9 e). Histologically, there weremeshes of P-selectin immunostained foci in the ILT predominantlyassociated with fibrin and leukocytes, rather than with foci where redblood cell predominated (hemogglutination) (FIG. 9 f).

An overtime course of the ΔNSE(%) for Group 1 is presented on FIG. 10.In the thrombus areas, ILSD could be detected as early as 15 minutesafter injection of USPIO-FUCO and was maximum 1 hour after injection (15min, p<0.05; 30 min, 45 min, 60 min, p<0.001). Thrombus thicknessmeasured on MR images 1 hour after USPIO-FUCO injection showed anexcellent correlation with histology at the corresponding level(r²=0.90) although MRI consistently overestimated thrombus thicknesscompared to histology. The minimal thickness of thrombus that could bedetected by MRI (FIG. 9 h) was 130 pm on histological section (FIG. 9i). No visual ILSD could be identified in rats from Group 2.

When comparing Group 1 and Group 2 in terms of luminal area before and 1hour after injection of the contrast agent, in the areas of thrombusidentified by histology, rats injected with USPIO-FUCO showed a largerarea reduction (ΔR%) than rats injected with USPIO-CMD (p<0.001) (FIG.12).

Ex vivo MRI. On images acquired with a short echo time (3.8 ms), aheterogeneous signal with meshes of signal drop similar was observed inthe thrombus areas similar to what was observed onP-selectin-immunostained slices. This heterogeneity was not visible athigher TE. On T2* maps, a large heterogeneity was observed.

Electron Microscopy. Confirmation of the presence of iron nanoparticlesin the thrombus was obtained using electron microscopy (FIG. 13). Ironnanoparticles were observed as a hyperdense signal, predominantly infibrin rich areas of the thrombus.

Discussion

The present example shows that, through P-selectin molecular imaging:USPIO-FUCO (1) allowed visualization of platelet-rich thrombus with highsensitivity in a rat model, (2) within 30 minutes after injection, and(3) with an excellent selectivity at a tissue level of adhesion andretention of the nanoparticles.

Relaxivity of the Contrast Agents. The relaxivities r1 and r2 were foundto be identical for both contrast agents at a given frequency. Theincrease in r2 from USPIO-CMD to USPIO-FUCO is in accordance with theincrease in size of the nanoparticles from 39.4 nm to 65.6 nm,respectively (Geraldes et al., Contrast Media Mol. Imaging, 2009, 4:1-23).

P-Selectin Targeted Imaging Agents. As demonstrated herein, USPIO-FUCOshows a high specificity for P-selectin. USPIOs are mostly used as MRIcontrast agents due to their negative enhancement effect on T2- andT2*-weighted sequences. However, in addition to the T2 and T2* effects,USPIOs also exhibit a T1 effect (Chambon et al., Magn. Reson. Imaging,1993, 11: 509-519; Canet et al., Magn. Reson. Imaging, 1993, 11:1139-1145). In the present study, there was no detectable T1 effect onthe aortic wall using either USPIO-FUCO or USPIO-CMD. The T2* effectusing USPIO-FUCO was however highly visible with a strong ILSD 1 hourafter injection in the area corresponding to the thrombus on histology.This strong ILSD was not visible after injection of USPIO-CMD,suggesting that USPIO-CMD might act like non-specific USPIOs which arephagocytized 24-48 hours after injection (Hyafil et al., Arterioscler.Thromb. Vasc. Biol., 2006, 26: 176-181; Ruehm et al., Circulation, 2001,103: 415-422).

Distribution of P-Selectin. Enlargement of abdominal aortic aneurysminvolves proteolytic degradation of media, adventitial inflammation andfibrosis, and the formation of an intraluminal thrombus. It has alsobeen suggested that the biological activity of ILT could be one of thedriving forces in aneurismal evolution (Michel et al., Cardiovasc. Res.,2011, 90: 18-27).

Interestingly, in the present MRI experiments, a high variability ofUSPIO-FUCO uptake within the thrombus was observed, with a heterogeneoussignal and T2* showing meshes of low signal and short T2* areas. Thisdistribution looked very similar to that observed by histology afterP-selectin immunostaining, suggesting the presence of higherconcentrations of USPIO-FUCO in areas rich in P-selectin-rich fibrinthan in RBC-rich areas. Unfortunately, due to the large difference inslice thickness between MRI and histology (125 μm and 5 μm,respectively), it was not possible to conclude definitely regarding thispoint.

Utility. Though it has been considered that targeted iron oxidemicroparticles detected by MRI requires an imaging duration of severalhours, in the present study, it took less than 30 minutes to depict anintravascular thrombus with high sensitivity. Since MRI is now the goldstandard (Takaya et al., Circulation, 2005, 111: 2768-2775) fordetecting intra-plaque hemorrhages in at risk atherothrombotic patients(Michel et al., Eur. Heart J., 2011, 32: 1977-1985), the use ofUSPIO-FUCO, which can detect P-selectin with high sensitivity, will be apowerful adjuvant for sensitizing MRI in the detection of vulnerableplaque.

Perl blue stain is an established method allowing detection of iron inbiological tissues. However, it cannot distinguish the origin (i.e.,endogenous or exogenous) of iron particles. In the present study,endogenous iron may result from the operational procedure used forcausing aneurysm and thrombus, and was confirmed on T2* weighted imagesbefore injection of the contrast agent. In the USPIO-FUCO nanoparticles,the fucoidan constitutes the outer-shell of the particles. In apreliminary experiment, USPIO inside USPIO-FUCO nanoparticles could notdetected using conventional Perl-Blue staining. This might be due to alarge number of electron charges around the fucoidan. Consequently,electron microscopy was used to confirm the ILT location of USPIO.

The fact that gradient echo MR sequences are more sensitive thanspin-echo sequences for detecting the contrast agent, results from theinherent T2* sensitivity of these sequences (Foster-Gareau et al., Magn.Reson. Med., 2003, 49: 968-971). Signal attenuation from USPIOs due totheir T2*/T2 effect can produce artifacts distorting the assessment ofthe size of the contrasted area (Corot et al., Adv. Drug Deliv. Rev.,2006, 58: 1471-1504). The degree of magnetic susceptibility effect(blooming effect) can be controlled by specifying data acquisitionparameters that have more or less T2 and T2* dependence. The extent ofsignal attenuation is not directly proportional to the concentration ofiron nanoparticles, because the blooming effect may extend to somedistance depending on the imaging parameters. Therefore, it could makethe actual size larger than the lesion. The present data confirm thispotential overestimation by showing, despite an excellent correlationbetween MRI and histology for thrombus thickness measurement (r²=0.90)(FIG. 11B), a consistently thicker ILT by MRI (p<0.0001). Fortunately,thanks to this overestimation, it is possible to detect very smallthrombi attached to the aortic wall with sizes as small as 100 μm (FIG.9 g-i). This might be very useful to detect culprit atheroscleroticplaques, in particular in stroke patients.

OTHER EMBODIMENTS

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of the specification or practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with the true scope of theinvention being indicated by the following claims.

1. An imaging agent comprising at least one fucoidan moiety associatedwith at least one detectable moiety, wherein the imaging agent isselectin-targeted.
 2. The selectin-targeted imaging agent according toclaim 1, wherein the at least one fucoidan moiety binds to at least onehuman selectin selected from the group consisting of P-selectin,L-selectin and E-selectin, with a dissociation constant of between about0.1 nM and about 500 nM.
 3. The selectin-targeted imaging agentaccording to claim 1, wherein the at least one detectable moietycomprises a metal-chelating moiety complexed to a detectable metalmoiety.
 4. The selectin-targeted imaging agent according to claim 1,wherein the at least one detectable moiety is detectable by planarscintigraphy (PS), Single Photon Emission Computed Tomography (SPECT),Positron Emission Tomography (PET), contrast-enhanced ultrasonography(CEUS), Magnetic Resonance Imaging (MRI), fluorescence spectroscopy,Computed Tomography, ultrasonography, X-ray radiography, or anycombination thereof.
 5. The selectin-targeted imaging agent according toclaim 1, wherein the at least one detectable moiety comprises a memberof the group consisting of: ultrasmall superparamagnetic iron oxideparticles (USPIOs), technetium-99m (^(99m)Tc), gallium-67 (⁶⁷Ga),yttrium-91 (⁹¹Y), indium-111 (¹¹¹In), rhenium-186 (¹⁸⁶Re), thallium-201(²⁰¹T1), carbon-11 (¹¹C), nitrogen-13 (¹³N), oxygen-15 (¹⁵O),fluorine-18 (¹⁸F), gadolinium III (Gd³⁺), chromium III (Cr³⁺),dysprosium III (Dy³⁺), europium (Eu³⁺), iron III (Fe³⁺), manganese II(Mn²⁺), ytterbium III (Yb³⁺), europium (Eu³⁺), quantum dots, Texas red,fluorescein isothiocyanate (FITC), phycoerythrin (PE), rhodamine,carboxycyanine, Cy-3, Cy-5, Cy5.5, Cy7, DY-630, DY-635, DY-680, Atto 565dyes, merocyanine, styryl dye, oxonol dye, BODIPY dyes, acousticallyactive microbubbles, acoustically active liposomes, iodine, andanalogues thereof, derivatives thereof, and combinations thereof.
 6. Theselectin-targeted imaging agent according to claim 1, wherein the atleast one fucoidan moiety has an average molecular weight of about 2000to about 8000 Da.
 7. The selectin-targeted imaging agent according toclaim 1, wherein the at least one fucoidan moiety has an averagemolecular weight of about 20,000 to about 70,000 Da.
 8. Theselectin-targeted imaging agent according to claim 1 wherein the atleast one fucoidan moiety has an average molecular weight of about100,000 to about 500,000 Da.
 9. The selectin-targeted imaging agentaccording to claim 1, wherein the at least one detectable moietycomprises an ultrasmall superparamagnetic iron oxide particle (USPIO)and the at least one fucoidan moiety and where the fucoidan moietyconstitutes a shell around the at least one USPIO.
 10. A pharmaceuticalcomposition comprising an effective amount of at least oneselectin-targeted imaging agent according to claim 1, or aphysiologically tolerable salt thereof, and at least onepharmaceutically acceptable carrier.
 11. The pharmaceutical compositionaccording to claim 10, wherein the at least one selectin-targetedimaging agent is a selectin-targeted imaging agent of claim
 9. 12. Amethod for diagnosing a clinical condition associated with selectins ina patient, said method comprising steps of: administering to the patientan effective amount of a pharmaceutical composition according to claim1, and detecting any selectin bound to the imaging agent using animaging technique.
 13. The method according to claim 12, wherein theclinical condition associated with selectins is a member of the groupconsisting of thrombosis, myocardial ischemia/reperfusion injury, strokeand ischemic brain trauma, neurodegenerative disorders, tumormetastasis, tumor growth, and rheumatoid arthritis.
 14. A method fordetecting the presence of abnormal selectins in a biological system, themethod comprising steps of: contacting the biological system with aneffective amount of a selectin-targeted imaging agent of claim 1, anddetecting any selectin bound to the imaging agent using an imagingtechnique.
 15. The method according to claim 14, wherein the biologicalsample is selected from the group consisting of a cell, a biologicalfluid and a biological tissue.
 16. The method according to claim 15,wherein the biological sample originates from a patient suspected ofhaving a clinical condition associated with selectins, and said methodis used to diagnose the clinical condition associated with selectins.17. The method according to claim 16, wherein the clinical conditionassociated with selectins is a member of the group consisting ofthrombosis, myocardial ischemia/reperfusion injury, stroke and ischemicbrain trauma, neurodegenerative disorders, tumor metastasis, tumorgrowth, and rheumatoid arthritis.
 18. The method according to claim 14,wherein the biological sample originates from a patient who has receiveda treatment for a clinical condition associated with selectins, and saidmethod is used to monitor the response of the patient to the treatment.19. The method according to claim 18, wherein the clinical conditionassociated with selectins is a member of the group consisting ofthrombosis, myocardial ischemia/reperfusion injury, stroke and ischemicbrain trauma, neurodegenerative disorders, tumor metastasis, tumorgrowth, and rheumatoid arthritis.
 20. A kit for the diagnosis of aclinical condition associated with selectins in a patient or for thedetection of abnormal selectins in a biological system, the kitcomprising: a selectin-targeted imaging agent according to claim 1, or afucoidan moiety, a detectable moiety, and instructions for preparing aselectin-targeted imaging agent according to claim
 1. 21. The kitaccording to claim 20, further comprising instructions for diagnosingthe clinical condition associated with selectins using theselectin-targeted imaging agent.
 22. The kit according to claim 21,wherein the clinical condition associated with selectins is a member ofthe group consisting of thrombosis, myocardial ischemia/reperfusioninjury, stroke and ischemic brain trauma, neurodegenerative disorders,tumor metastasis, tumor growth, and rheumatoid arthritis.
 23. The kitaccording to claim 21, further comprising instructions for detectingabnormal selectins in the biological system using the selectin-targetedimaging agent.